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 $211.26   10.442%   $233.3198   $233.32   $233.30   $233.30  
  Purchase #2 $176.75   8.552%   $191.8657   $191.87   $191.85   $191.90  
  Purchase #3 $210.33   9.703%   $230.7383   $230.74   $230.75   $230.70  
  Purchase #4 $212.60   9.683%   $233.1861   $233.19   $233.20   $233.20  
  Purchase #5 $109.90   3.481%   $113.7256   $113.73   $113.75   $113.70  
  Purchase #6 $143.35   9.345%   $156.7461   $156.75   $156.75   $156.70  
  Purchase #7 $136.83   5.338%   $144.134   $144.13   $144.15   $144.10  
  7 purchase totals = $1,201.02       $1,303.7156   $1,303.73   $1,303.75   $1,303.60