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 $55.32   4.155%   $57.6185   $57.62   $57.60   $57.60  
  Purchase #2 $216.86   9.189%   $236.7873   $236.79   $236.80   $236.80  
  Purchase #3 $195.95   11.578%   $218.6371   $218.64   $218.65   $218.60  
  Purchase #4 $73.57   12.571%   $82.8185   $82.82   $82.80   $82.80  
  Purchase #5 $10.69   6.417%   $11.376   $11.38   $11.40   $11.40  
  Purchase #6 $248.37   7.413%   $266.7817   $266.78   $266.80   $266.80  
  Purchase #7 $218.60   6.248%   $232.2581   $232.26   $232.25   $232.30  
  7 purchase totals = $1,019.36       $1,106.2772   $1,106.29   $1,106.30   $1,106.30