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 $209.82   11.398%   $233.7353   $233.74   $233.75   $233.70  
  Purchase #2 $48.51   4.579%   $50.7313   $50.73   $50.75   $50.70  
  Purchase #3 $139.47   9.313%   $152.4588   $152.46   $152.45   $152.50  
  Purchase #4 $114.74   7.589%   $123.4476   $123.45   $123.45   $123.40  
  Purchase #5 $59.93   3.782%   $62.1966   $62.20   $62.20   $62.20  
  Purchase #6 $222.55   8.606%   $241.7027   $241.70   $241.70   $241.70  
  Purchase #7 $235.68   7.426%   $253.1816   $253.18   $253.20   $253.20  
  7 purchase totals = $1,030.70       $1,117.4539   $1,117.46   $1,117.50   $1,117.40