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 $83.51   10.381%   $92.1792   $92.18   $92.20   $92.20  
  Purchase #2 $10.77   6.334%   $11.4522   $11.45   $11.45   $11.50  
  Purchase #3 $148.82   13.328%   $168.6547   $168.65   $168.65   $168.70  
  Purchase #4 $229.37   6.683%   $244.6988   $244.70   $244.70   $244.70  
  Purchase #5 $148.83   8.858%   $162.0134   $162.01   $162.00   $162.00  
  Purchase #6 $133.26   11.825%   $149.018   $149.02   $149.00   $149.00  
  Purchase #7 $120.87   12.180%   $135.592   $135.59   $135.60   $135.60  
  7 purchase totals = $875.43       $963.6083   $963.60   $963.60   $963.70