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 $50.76   3.802%   $52.6899   $52.69   $52.70   $52.70  
  Purchase #2 $191.44   6.822%   $204.5   $204.50   $204.50   $204.50  
  Purchase #3 $24.71   3.804%   $25.65   $25.65   $25.65   $25.70  
  Purchase #4 $245.60   5.534%   $259.1915   $259.19   $259.20   $259.20  
  Purchase #5 $127.78   5.695%   $135.0571   $135.06   $135.05   $135.10  
  Purchase #6 $246.29   6.550%   $262.422   $262.42   $262.40   $262.40  
  Purchase #7 $43.29   5.453%   $45.6506   $45.65   $45.65   $45.70  
  7 purchase totals = $929.87       $985.1611   $985.16   $985.15   $985.30