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 $201.54   11.460%   $224.6365   $224.64   $224.65   $224.60  
  Purchase #2 $119.75   5.827%   $126.7278   $126.73   $126.75   $126.70  
  Purchase #3 $134.61   4.643%   $140.8599   $140.86   $140.85   $140.90  
  Purchase #4 $109.46   9.508%   $119.8675   $119.87   $119.85   $119.90  
  Purchase #5 $8.46   4.362%   $8.829   $8.83   $8.85   $8.80  
  Purchase #6 $201.80   13.814%   $229.6767   $229.68   $229.70   $229.70  
  Purchase #7 $99.93   9.312%   $109.2355   $109.24   $109.25   $109.20  
  7 purchase totals = $875.55       $959.8329   $959.85   $959.90   $959.80