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 $48.61   13.143%   $54.9988   $55.00   $55.00   $55.00  
  Purchase #2 $108.97   4.215%   $113.5631   $113.56   $113.55   $113.60  
  Purchase #3 $99.53   12.564%   $112.0349   $112.03   $112.05   $112.00  
  Purchase #4 $125.55   6.454%   $133.653   $133.65   $133.65   $133.70  
  Purchase #5 $122.32   12.429%   $137.5232   $137.52   $137.50   $137.50  
  Purchase #6 $138.75   9.545%   $151.9937   $151.99   $152.00   $152.00  
  Purchase #7 $194.53   4.332%   $202.957   $202.96   $202.95   $203.00  
  7 purchase totals = $838.26       $906.7237   $906.71   $906.70   $906.80