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 $60.34   11.589%   $67.3328   $67.33   $67.35   $67.30  
  Purchase #2 $86.53   6.619%   $92.2574   $92.26   $92.25   $92.30  
  Purchase #3 $180.95   12.159%   $202.9517   $202.95   $202.95   $203.00  
  Purchase #4 $113.45   8.511%   $123.1057   $123.11   $123.10   $123.10  
  Purchase #5 $15.89   12.148%   $17.8203   $17.82   $17.80   $17.80  
  Purchase #6 $129.50   7.520%   $139.2384   $139.24   $139.25   $139.20  
  Purchase #7 $85.65   7.633%   $92.1877   $92.19   $92.20   $92.20  
  7 purchase totals = $672.31       $734.8940   $734.90   $734.90   $734.90