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 $142.84   8.263%   $154.6429   $154.64   $154.65   $154.60  
  Purchase #2 $170.74   5.587%   $180.2792   $180.28   $180.30   $180.30  
  Purchase #3 $182.77   12.509%   $205.6327   $205.63   $205.65   $205.60  
  Purchase #4 $88.81   6.276%   $94.3837   $94.38   $94.40   $94.40  
  Purchase #5 $234.66   13.811%   $267.0689   $267.07   $267.05   $267.10  
  Purchase #6 $5.41   13.418%   $6.1359   $6.14   $6.15   $6.10  
  Purchase #7 $130.61   11.245%   $145.2971   $145.30   $145.30   $145.30  
  7 purchase totals = $955.84       $1,053.4404   $1,053.44   $1,053.50   $1,053.40