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 $202.36   11.828%   $226.2951   $226.30   $226.30   $226.30  
  Purchase #2 $173.75   4.386%   $181.3707   $181.37   $181.35   $181.40  
  Purchase #3 $19.98   4.585%   $20.8961   $20.90   $20.90   $20.90  
  Purchase #4 $130.78   12.299%   $146.8646   $146.86   $146.85   $146.90  
  Purchase #5 $62.36   8.452%   $67.6307   $67.63   $67.65   $67.60  
  Purchase #6 $147.53   6.278%   $156.7919   $156.79   $156.80   $156.80  
  Purchase #7 $200.40   5.484%   $211.3899   $211.39   $211.40   $211.40  
  7 purchase totals = $937.16       $1,011.2390   $1,011.24   $1,011.25   $1,011.30