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 $192.28   8.557%   $208.7334   $208.73   $208.75   $208.70  
  Purchase #2 $30.32   13.191%   $34.3195   $34.32   $34.30   $34.30  
  Purchase #3 $120.37   7.693%   $129.6301   $129.63   $129.65   $129.60  
  Purchase #4 $101.31   4.390%   $105.7575   $105.76   $105.75   $105.80  
  Purchase #5 $225.61   9.375%   $246.7609   $246.76   $246.75   $246.80  
  Purchase #6 $137.34   4.443%   $143.442   $143.44   $143.45   $143.40  
  Purchase #7 $210.98   12.387%   $237.1141   $237.11   $237.10   $237.10  
  7 purchase totals = $1,018.21       $1,105.7575   $1,105.75   $1,105.75   $1,105.70