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 $168.39   11.391%   $187.5713   $187.57   $187.55   $187.60  
  Purchase #2 $188.55   4.809%   $197.6174   $197.62   $197.60   $197.60  
  Purchase #3 $47.45   12.118%   $53.2   $53.20   $53.20   $53.20  
  Purchase #4 $190.44   4.523%   $199.0536   $199.05   $199.05   $199.10  
  Purchase #5 $63.49   6.571%   $67.6619   $67.66   $67.65   $67.70  
  Purchase #6 $203.57   10.228%   $224.3911   $224.39   $224.40   $224.40  
  Purchase #7 $240.70   6.372%   $256.0374   $256.04   $256.05   $256.00  
  7 purchase totals = $1,102.59       $1,185.5327   $1,185.53   $1,185.50   $1,185.60