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 $126.28   6.316%   $134.2558   $134.26   $134.25   $134.30  
  Purchase #2 $172.29   8.342%   $186.6624   $186.66   $186.65   $186.70  
  Purchase #3 $96.68   11.591%   $107.8862   $107.89   $107.90   $107.90  
  Purchase #4 $169.63   4.254%   $176.8461   $176.85   $176.85   $176.80  
  Purchase #5 $201.34   4.606%   $210.6137   $210.61   $210.60   $210.60  
  Purchase #6 $116.53   10.280%   $128.5093   $128.51   $128.50   $128.50  
  Purchase #7 $186.52   8.858%   $203.0419   $203.04   $203.05   $203.00  
  7 purchase totals = $1,069.27       $1,147.8154   $1,147.82   $1,147.80   $1,147.80