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 $47.63   8.326%   $51.5957   $51.60   $51.60   $51.60  
  Purchase #2 $216.69   11.547%   $241.7112   $241.71   $241.70   $241.70  
  Purchase #3 $249.27   12.392%   $280.1595   $280.16   $280.15   $280.20  
  Purchase #4 $81.29   9.513%   $89.0231   $89.02   $89.00   $89.00  
  Purchase #5 $101.45   12.713%   $114.3473   $114.35   $114.35   $114.30  
  Purchase #6 $125.40   4.259%   $130.7408   $130.74   $130.75   $130.70  
  Purchase #7 $169.36   4.687%   $177.2979   $177.30   $177.30   $177.30  
  7 purchase totals = $991.09       $1,084.8755   $1,084.88   $1,084.85   $1,084.80