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 $168.69   8.596%   $183.1906   $183.19   $183.20   $183.20  
  Purchase #2 $219.94   8.457%   $238.5403   $238.54   $238.55   $238.50  
  Purchase #3 $24.32   11.480%   $27.1119   $27.11   $27.10   $27.10  
  Purchase #4 $135.99   12.538%   $153.0404   $153.04   $153.05   $153.00  
  Purchase #5 $81.66   9.488%   $89.4079   $89.41   $89.40   $89.40  
  Purchase #6 $140.76   12.349%   $158.1425   $158.14   $158.15   $158.10  
  Purchase #7 $177.27   5.657%   $187.2982   $187.30   $187.30   $187.30  
  7 purchase totals = $948.63       $1,036.7318   $1,036.73   $1,036.75   $1,036.60