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 $202.29   11.179%   $224.904   $224.90   $224.90   $224.90  
  Purchase #2 $72.29   6.561%   $77.0329   $77.03   $77.05   $77.00  
  Purchase #3 $19.94   4.805%   $20.8981   $20.90   $20.90   $20.90  
  Purchase #4 $56.97   13.193%   $64.4861   $64.49   $64.50   $64.50  
  Purchase #5 $197.27   8.170%   $213.387   $213.39   $213.40   $213.40  
  Purchase #6 $77.40   4.606%   $80.965   $80.97   $80.95   $81.00  
  Purchase #7 $34.41   13.836%   $39.171   $39.17   $39.15   $39.20  
  7 purchase totals = $660.57       $720.8441   $720.85   $720.85   $720.90