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 $212.27   11.873%   $237.4728   $237.47   $237.45   $237.50  
  Purchase #2 $206.64   12.730%   $232.9453   $232.95   $232.95   $232.90  
  Purchase #3 $23.47   7.244%   $25.1702   $25.17   $25.15   $25.20  
  Purchase #4 $133.87   5.527%   $141.269   $141.27   $141.25   $141.30  
  Purchase #5 $175.34   11.560%   $195.6093   $195.61   $195.60   $195.60  
  Purchase #6 $140.26   9.120%   $153.0517   $153.05   $153.05   $153.10  
  Purchase #7 $59.90   12.476%   $67.3731   $67.37   $67.35   $67.40  
  7 purchase totals = $951.75       $1,052.8914   $1,052.89   $1,052.80   $1,053.00