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 $57.95   8.772%   $63.0334   $63.03   $63.05   $63.00  
  Purchase #2 $113.52   13.390%   $128.7203   $128.72   $128.70   $128.70  
  Purchase #3 $97.51   5.655%   $103.0242   $103.02   $103.00   $103.00  
  Purchase #4 $218.82   3.252%   $225.936   $225.94   $225.95   $225.90  
  Purchase #5 $35.50   13.826%   $40.4082   $40.41   $40.40   $40.40  
  Purchase #6 $139.83   13.127%   $158.1855   $158.19   $158.20   $158.20  
  Purchase #7 $58.45   13.317%   $66.2338   $66.23   $66.25   $66.20  
  7 purchase totals = $721.58       $785.5414   $785.54   $785.55   $785.40