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 $49.46   7.737%   $53.2867   $53.29   $53.30   $53.30  
  Purchase #2 $31.62   6.635%   $33.718   $33.72   $33.70   $33.70  
  Purchase #3 $28.53   9.315%   $31.1876   $31.19   $31.20   $31.20  
  Purchase #4 $96.39   6.590%   $102.7421   $102.74   $102.75   $102.70  
  Purchase #5 $249.53   7.398%   $267.9902   $267.99   $268.00   $268.00  
  Purchase #6 $185.38   11.183%   $206.111   $206.11   $206.10   $206.10  
  Purchase #7 $91.28   5.674%   $96.4592   $96.46   $96.45   $96.50  
  7 purchase totals = $732.19       $791.4948   $791.50   $791.50   $791.50