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 $236.28   13.210%   $267.4926   $267.49   $267.50   $267.50  
  Purchase #2 $221.67   6.612%   $236.3268   $236.33   $236.35   $236.30  
  Purchase #3 $88.26   13.135%   $99.853   $99.85   $99.85   $99.90  
  Purchase #4 $36.68   8.158%   $39.6724   $39.67   $39.65   $39.70  
  Purchase #5 $246.34   10.196%   $271.4568   $271.46   $271.45   $271.50  
  Purchase #6 $98.66   3.113%   $101.7313   $101.73   $101.75   $101.70  
  Purchase #7 $230.77   6.141%   $244.9416   $244.94   $244.95   $244.90  
  7 purchase totals = $1,158.66       $1,261.4745   $1,261.47   $1,261.50   $1,261.50