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 $119.71   12.463%   $134.6295   $134.63   $134.65   $134.60  
  Purchase #2 $54.36   6.172%   $57.7151   $57.72   $57.70   $57.70  
  Purchase #3 $60.43   3.162%   $62.3408   $62.34   $62.35   $62.30  
  Purchase #4 $206.94   12.436%   $232.6751   $232.68   $232.70   $232.70  
  Purchase #5 $26.46   6.198%   $28.1   $28.10   $28.10   $28.10  
  Purchase #6 $200.70   13.650%   $228.0956   $228.10   $228.10   $228.10  
  Purchase #7 $133.52   8.105%   $144.3418   $144.34   $144.35   $144.30  
  7 purchase totals = $802.12       $887.8979   $887.91   $887.95   $887.80