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 $203.99   10.451%   $225.309   $225.31   $225.30   $225.30  
  Purchase #2 $206.95   3.227%   $213.6283   $213.63   $213.65   $213.60  
  Purchase #3 $212.66   7.649%   $228.9264   $228.93   $228.95   $228.90  
  Purchase #4 $194.41   9.381%   $212.6476   $212.65   $212.65   $212.60  
  Purchase #5 $133.96   7.868%   $144.5   $144.50   $144.50   $144.50  
  Purchase #6 $205.65   3.296%   $212.4282   $212.43   $212.45   $212.40  
  Purchase #7 $13.38   3.778%   $13.8855   $13.89   $13.90   $13.90  
  7 purchase totals = $1,171.00       $1,251.3250   $1,251.34   $1,251.40   $1,251.20