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 $26.98   7.345%   $28.9617   $28.96   $28.95   $29.00  
  Purchase #2 $219.38   8.238%   $237.4525   $237.45   $237.45   $237.50  
  Purchase #3 $32.76   8.652%   $35.5944   $35.59   $35.60   $35.60  
  Purchase #4 $181.82   12.613%   $204.753   $204.75   $204.75   $204.80  
  Purchase #5 $79.71   10.123%   $87.779   $87.78   $87.80   $87.80  
  Purchase #6 $189.81   13.427%   $215.2958   $215.30   $215.30   $215.30  
  Purchase #7 $54.77   13.262%   $62.0336   $62.03   $62.05   $62.00  
  7 purchase totals = $785.23       $871.8700   $871.86   $871.90   $872.00