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 $41.69   3.822%   $43.2834   $43.28   $43.30   $43.30  
  Purchase #2 $14.94   8.293%   $16.179   $16.18   $16.20   $16.20  
  Purchase #3 $235.98   10.831%   $261.539   $261.54   $261.55   $261.50  
  Purchase #4 $62.30   8.632%   $67.6777   $67.68   $67.70   $67.70  
  Purchase #5 $69.36   3.308%   $71.6544   $71.65   $71.65   $71.70  
  Purchase #6 $232.82   10.317%   $256.84   $256.84   $256.85   $256.80  
  Purchase #7 $75.76   9.719%   $83.1231   $83.12   $83.10   $83.10  
  7 purchase totals = $732.85       $800.2966   $800.29   $800.35   $800.30