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 $245.28   12.568%   $276.1068   $276.11   $276.10   $276.10  
  Purchase #2 $84.95   12.258%   $95.3632   $95.36   $95.35   $95.40  
  Purchase #3 $38.51   6.428%   $40.9854   $40.99   $41.00   $41.00  
  Purchase #4 $94.70   7.734%   $102.0241   $102.02   $102.00   $102.00  
  Purchase #5 $103.62   10.829%   $114.841   $114.84   $114.85   $114.80  
  Purchase #6 $94.57   7.307%   $101.4802   $101.48   $101.50   $101.50  
  Purchase #7 $5.93   6.223%   $6.299   $6.30   $6.30   $6.30  
  7 purchase totals = $667.56       $737.0997   $737.10   $737.10   $737.10