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 $84.42   3.733%   $87.5714   $87.57   $87.55   $87.60  
  Purchase #2 $119.47   11.858%   $133.6368   $133.64   $133.65   $133.60  
  Purchase #3 $205.26   4.191%   $213.8624   $213.86   $213.85   $213.90  
  Purchase #4 $238.92   11.593%   $266.618   $266.62   $266.60   $266.60  
  Purchase #5 $190.47   3.211%   $196.586   $196.59   $196.60   $196.60  
  Purchase #6 $210.58   3.755%   $218.4873   $218.49   $218.50   $218.50  
  Purchase #7 $39.86   11.719%   $44.5312   $44.53   $44.55   $44.50  
  7 purchase totals = $1,088.98       $1,161.2931   $1,161.30   $1,161.30   $1,161.30