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 $107.78   10.588%   $119.1917   $119.19   $119.20   $119.20  
  Purchase #2 $250.56   8.797%   $272.6018   $272.60   $272.60   $272.60  
  Purchase #3 $96.47   12.354%   $108.3879   $108.39   $108.40   $108.40  
  Purchase #4 $152.84   11.637%   $170.626   $170.63   $170.65   $170.60  
  Purchase #5 $184.96   7.728%   $199.2537   $199.25   $199.25   $199.30  
  Purchase #6 $16.62   4.575%   $17.3804   $17.38   $17.40   $17.40  
  Purchase #7 $146.76   8.743%   $159.5912   $159.59   $159.60   $159.60  
  7 purchase totals = $955.99       $1,047.0327   $1,047.03   $1,047.10   $1,047.10