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 $53.49   12.557%   $60.2067   $60.21   $60.20   $60.20  
  Purchase #2 $207.57   9.418%   $227.1189   $227.12   $227.10   $227.10  
  Purchase #3 $107.48   13.234%   $121.7039   $121.70   $121.70   $121.70  
  Purchase #4 $44.33   6.383%   $47.1596   $47.16   $47.15   $47.20  
  Purchase #5 $124.55   13.393%   $141.231   $141.23   $141.25   $141.20  
  Purchase #6 $44.58   4.179%   $46.443   $46.44   $46.45   $46.40  
  Purchase #7 $157.34   9.615%   $172.4682   $172.47   $172.45   $172.50  
  7 purchase totals = $739.34       $816.3313   $816.33   $816.30   $816.30