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 $38.46   12.395%   $43.2271   $43.23   $43.25   $43.20  
  Purchase #2 $200.88   9.114%   $219.1882   $219.19   $219.20   $219.20  
  Purchase #3 $121.79   8.844%   $132.5611   $132.56   $132.55   $132.60  
  Purchase #4 $162.69   5.569%   $171.7502   $171.75   $171.75   $171.80  
  Purchase #5 $143.78   3.201%   $148.3824   $148.38   $148.40   $148.40  
  Purchase #6 $202.48   7.425%   $217.5141   $217.51   $217.50   $217.50  
  Purchase #7 $75.96   9.660%   $83.2977   $83.30   $83.30   $83.30  
  7 purchase totals = $946.04       $1,015.9208   $1,015.92   $1,015.95   $1,016.00