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 $89.69   5.645%   $94.753   $94.75   $94.75   $94.80  
  Purchase #2 $29.49   13.562%   $33.4894   $33.49   $33.50   $33.50  
  Purchase #3 $75.86   3.185%   $78.2761   $78.28   $78.30   $78.30  
  Purchase #4 $229.66   12.139%   $257.5384   $257.54   $257.55   $257.50  
  Purchase #5 $69.52   9.115%   $75.8567   $75.86   $75.85   $75.90  
  Purchase #6 $239.43   3.807%   $248.5451   $248.55   $248.55   $248.50  
  Purchase #7 $94.58   8.541%   $102.6581   $102.66   $102.65   $102.70  
  7 purchase totals = $828.23       $891.1168   $891.13   $891.15   $891.20