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 $36.46   12.467%   $41.0055   $41.01   $41.00   $41.00  
  Purchase #2 $186.47   10.294%   $205.6652   $205.67   $205.65   $205.70  
  Purchase #3 $63.28   5.301%   $66.6345   $66.63   $66.65   $66.60  
  Purchase #4 $146.81   3.464%   $151.8955   $151.90   $151.90   $151.90  
  Purchase #5 $186.31   13.683%   $211.8028   $211.80   $211.80   $211.80  
  Purchase #6 $213.56   5.141%   $224.5391   $224.54   $224.55   $224.50  
  Purchase #7 $32.60   7.519%   $35.0512   $35.05   $35.05   $35.10  
  7 purchase totals = $865.49       $936.5938   $936.60   $936.60   $936.60