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 $216.48   11.315%   $240.9747   $240.97   $240.95   $241.00  
  Purchase #2 $94.25   4.695%   $98.675   $98.68   $98.70   $98.70  
  Purchase #3 $123.57   5.847%   $130.7951   $130.80   $130.80   $130.80  
  Purchase #4 $120.72   10.738%   $133.6829   $133.68   $133.70   $133.70  
  Purchase #5 $211.63   13.227%   $239.6223   $239.62   $239.60   $239.60  
  Purchase #6 $7.66   6.146%   $8.1308   $8.13   $8.15   $8.10  
  Purchase #7 $161.51   4.492%   $168.765   $168.77   $168.75   $168.80  
  7 purchase totals = $935.82       $1,020.6458   $1,020.65   $1,020.65   $1,020.70