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 $89.48   8.267%   $96.8773   $96.88   $96.90   $96.90  
  Purchase #2 $68.39   9.816%   $75.1032   $75.10   $75.10   $75.10  
  Purchase #3 $247.96   3.340%   $256.2419   $256.24   $256.25   $256.20  
  Purchase #4 $154.26   9.598%   $169.0659   $169.07   $169.05   $169.10  
  Purchase #5 $53.43   8.125%   $57.7712   $57.77   $57.75   $57.80  
  Purchase #6 $119.71   12.115%   $134.2129   $134.21   $134.20   $134.20  
  Purchase #7 $203.72   3.385%   $210.6159   $210.62   $210.60   $210.60  
  7 purchase totals = $936.95       $999.8883   $999.89   $999.85   $999.90