Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $162.81   8.479%   $176.6147   $176.61   $176.60   $176.60  
  Purchase #2 $210.41   6.564%   $224.2213   $224.22   $224.20   $224.20  
  Purchase #3 $171.35   8.537%   $185.9781   $185.98   $186.00   $186.00  
  Purchase #4 $151.89   4.854%   $159.2627   $159.26   $159.25   $159.30  
  Purchase #5 $162.98   8.564%   $176.9376   $176.94   $176.95   $176.90  
  Purchase #6 $165.98   12.452%   $186.6478   $186.65   $186.65   $186.60  
  Purchase #7 $169.37   9.702%   $185.8023   $185.80   $185.80   $185.80  
  7 purchase totals = $1,194.79       $1,295.4645   $1,295.46   $1,295.45   $1,295.40