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 $48.61   7.448%   $52.2305   $52.23   $52.25   $52.20  
  Purchase #2 $93.46   10.315%   $103.1004   $103.10   $103.10   $103.10  
  Purchase #3 $43.26   6.366%   $46.0139   $46.01   $46.00   $46.00  
  Purchase #4 $97.51   6.786%   $104.127   $104.13   $104.15   $104.10  
  Purchase #5 $227.48   6.352%   $241.9295   $241.93   $241.95   $241.90  
  Purchase #6 $168.39   3.162%   $173.7145   $173.71   $173.70   $173.70  
  Purchase #7 $211.62   3.250%   $218.4977   $218.50   $218.50   $218.50  
  7 purchase totals = $890.33       $939.6135   $939.61   $939.65   $939.50