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 $94.63   10.380%   $104.4526   $104.45   $104.45   $104.50  
  Purchase #2 $161.84   6.197%   $171.8692   $171.87   $171.85   $171.90  
  Purchase #3 $198.56   7.541%   $213.5334   $213.53   $213.55   $213.50  
  Purchase #4 $94.73   3.757%   $98.289   $98.29   $98.30   $98.30  
  Purchase #5 $212.94   11.273%   $236.9447   $236.94   $236.95   $236.90  
  Purchase #6 $241.33   10.847%   $267.5071   $267.51   $267.50   $267.50  
  Purchase #7 $96.41   11.741%   $107.7295   $107.73   $107.75   $107.70  
  7 purchase totals = $1,100.44       $1,200.3255   $1,200.32   $1,200.35   $1,200.30