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 $209.97   7.593%   $225.913   $225.91   $225.90   $225.90  
  Purchase #2 $11.98   12.631%   $13.4932   $13.49   $13.50   $13.50  
  Purchase #3 $209.74   6.692%   $223.7758   $223.78   $223.80   $223.80  
  Purchase #4 $234.62   6.695%   $250.3278   $250.33   $250.35   $250.30  
  Purchase #5 $140.35   12.429%   $157.7941   $157.79   $157.80   $157.80  
  Purchase #6 $208.29   10.534%   $230.2313   $230.23   $230.25   $230.20  
  Purchase #7 $225.46   8.811%   $245.3253   $245.33   $245.35   $245.30  
  7 purchase totals = $1,240.41       $1,346.8605   $1,346.86   $1,346.95   $1,346.80