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 $54.83   10.217%   $60.432   $60.43   $60.45   $60.40  
  Purchase #2 $183.85   13.577%   $208.8113   $208.81   $208.80   $208.80  
  Purchase #3 $92.63   6.717%   $98.852   $98.85   $98.85   $98.90  
  Purchase #4 $205.82   3.412%   $212.8426   $212.84   $212.85   $212.80  
  Purchase #5 $65.45   8.429%   $70.9668   $70.97   $70.95   $71.00  
  Purchase #6 $58.46   10.476%   $64.5843   $64.58   $64.60   $64.60  
  Purchase #7 $178.29   7.493%   $191.6493   $191.65   $191.65   $191.60  
  7 purchase totals = $839.33       $908.1383   $908.13   $908.15   $908.10