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 $215.77   6.132%   $229.001   $229.00   $229.00   $229.00  
  Purchase #2 $61.49   7.679%   $66.2118   $66.21   $66.20   $66.20  
  Purchase #3 $32.50   8.840%   $35.373   $35.37   $35.35   $35.40  
  Purchase #4 $246.98   4.651%   $258.467   $258.47   $258.45   $258.50  
  Purchase #5 $222.52   13.748%   $253.112   $253.11   $253.10   $253.10  
  Purchase #6 $119.83   8.318%   $129.7975   $129.80   $129.80   $129.80  
  Purchase #7 $178.34   12.499%   $200.6307   $200.63   $200.65   $200.60  
  7 purchase totals = $1,077.43       $1,172.5930   $1,172.59   $1,172.55   $1,172.60