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 $92.63   6.117%   $98.2962   $98.30   $98.30   $98.30  
  Purchase #2 $114.26   13.446%   $129.6234   $129.62   $129.60   $129.60  
  Purchase #3 $189.38   7.107%   $202.8392   $202.84   $202.85   $202.80  
  Purchase #4 $224.48   11.192%   $249.6038   $249.60   $249.60   $249.60  
  Purchase #5 $65.88   12.406%   $74.0531   $74.05   $74.05   $74.10  
  Purchase #6 $153.79   8.474%   $166.8222   $166.82   $166.80   $166.80  
  Purchase #7 $105.55   4.400%   $110.1942   $110.19   $110.20   $110.20  
  7 purchase totals = $945.97       $1,031.4321   $1,031.42   $1,031.40   $1,031.40