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 $50.78   5.257%   $53.4495   $53.45   $53.45   $53.40  
  Purchase #2 $184.33   6.115%   $195.6018   $195.60   $195.60   $195.60  
  Purchase #3 $181.94   6.377%   $193.5423   $193.54   $193.55   $193.50  
  Purchase #4 $31.67   8.302%   $34.2992   $34.30   $34.30   $34.30  
  Purchase #5 $84.46   11.776%   $94.406   $94.41   $94.40   $94.40  
  Purchase #6 $151.51   4.717%   $158.6567   $158.66   $158.65   $158.70  
  Purchase #7 $28.86   11.712%   $32.2401   $32.24   $32.25   $32.20  
  7 purchase totals = $713.55       $762.1956   $762.20   $762.20   $762.10