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 $54.80   10.505%   $60.5567   $60.56   $60.55   $60.60  
  Purchase #2 $86.66   12.453%   $97.4518   $97.45   $97.45   $97.50  
  Purchase #3 $186.47   4.601%   $195.0495   $195.05   $195.05   $195.00  
  Purchase #4 $74.84   9.686%   $82.089   $82.09   $82.10   $82.10  
  Purchase #5 $71.63   10.793%   $79.361   $79.36   $79.35   $79.40  
  Purchase #6 $238.58   12.443%   $268.2665   $268.27   $268.25   $268.30  
  Purchase #7 $240.30   6.619%   $256.2055   $256.21   $256.20   $256.20  
  7 purchase totals = $953.28       $1,038.9800   $1,038.99   $1,038.95   $1,039.10