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 $58.67   6.220%   $62.3193   $62.32   $62.30   $62.30  
  Purchase #2 $207.94   10.300%   $229.3578   $229.36   $229.35   $229.40  
  Purchase #3 $5.29   3.504%   $5.4754   $5.48   $5.50   $5.50  
  Purchase #4 $94.52   8.227%   $102.2962   $102.30   $102.30   $102.30  
  Purchase #5 $209.84   13.229%   $237.5997   $237.60   $237.60   $237.60  
  Purchase #6 $105.65   6.814%   $112.849   $112.85   $112.85   $112.80  
  Purchase #7 $166.48   3.703%   $172.6448   $172.64   $172.65   $172.60  
  7 purchase totals = $848.39       $922.5422   $922.55   $922.55   $922.50