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 $91.47   13.475%   $103.7956   $103.80   $103.80   $103.80  
  Purchase #2 $184.89   5.269%   $194.6319   $194.63   $194.65   $194.60  
  Purchase #3 $157.40   7.129%   $168.621   $168.62   $168.60   $168.60  
  Purchase #4 $76.98   9.571%   $84.3478   $84.35   $84.35   $84.30  
  Purchase #5 $10.64   9.477%   $11.6484   $11.65   $11.65   $11.60  
  Purchase #6 $148.61   10.392%   $164.0536   $164.05   $164.05   $164.10  
  Purchase #7 $245.70   9.543%   $269.1472   $269.15   $269.15   $269.10  
  7 purchase totals = $915.69       $996.2455   $996.25   $996.25   $996.10