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 $15.99   7.796%   $17.2366   $17.24   $17.25   $17.20  
  Purchase #2 $117.99   9.595%   $129.3111   $129.31   $129.30   $129.30  
  Purchase #3 $75.66   11.554%   $84.4018   $84.40   $84.40   $84.40  
  Purchase #4 $148.59   10.507%   $164.2024   $164.20   $164.20   $164.20  
  Purchase #5 $222.36   9.254%   $242.9372   $242.94   $242.95   $242.90  
  Purchase #6 $107.39   10.780%   $118.9666   $118.97   $118.95   $119.00  
  Purchase #7 $240.56   13.500%   $273.0356   $273.04   $273.05   $273.00  
  7 purchase totals = $928.54       $1,030.0913   $1,030.10   $1,030.10   $1,030.00