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 $54.67   13.417%   $62.0051   $62.01   $62.00   $62.00  
  Purchase #2 $170.60   4.587%   $178.4254   $178.43   $178.45   $178.40  
  Purchase #3 $235.47   5.383%   $248.1454   $248.15   $248.15   $248.10  
  Purchase #4 $130.94   7.199%   $140.3664   $140.37   $140.35   $140.40  
  Purchase #5 $42.98   3.365%   $44.4263   $44.43   $44.45   $44.40  
  Purchase #6 $48.47   6.814%   $51.7727   $51.77   $51.75   $51.80  
  Purchase #7 $93.92   8.253%   $101.6712   $101.67   $101.65   $101.70  
  7 purchase totals = $777.05       $826.8125   $826.83   $826.80   $826.80