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 $64.34   11.107%   $71.4862   $71.49   $71.50   $71.50  
  Purchase #2 $83.92   5.560%   $88.586   $88.59   $88.60   $88.60  
  Purchase #3 $69.43   4.639%   $72.6509   $72.65   $72.65   $72.70  
  Purchase #4 $212.75   4.219%   $221.7259   $221.73   $221.75   $221.70  
  Purchase #5 $127.25   4.753%   $133.2982   $133.30   $133.30   $133.30  
  Purchase #6 $208.25   8.541%   $226.0366   $226.04   $226.05   $226.00  
  Purchase #7 $125.41   13.619%   $142.4896   $142.49   $142.50   $142.50  
  7 purchase totals = $891.35       $956.2734   $956.29   $956.35   $956.30