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 $87.57   12.446%   $98.469   $98.47   $98.45   $98.50  
  Purchase #2 $126.37   6.550%   $134.6472   $134.65   $134.65   $134.60  
  Purchase #3 $63.67   4.662%   $66.6383   $66.64   $66.65   $66.60  
  Purchase #4 $197.84   4.361%   $206.4678   $206.47   $206.45   $206.50  
  Purchase #5 $114.64   9.679%   $125.736   $125.74   $125.75   $125.70  
  Purchase #6 $116.38   7.397%   $124.9886   $124.99   $125.00   $125.00  
  Purchase #7 $31.60   8.227%   $34.1997   $34.20   $34.20   $34.20  
  7 purchase totals = $738.07       $791.1466   $791.16   $791.15   $791.10