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 $203.69   11.386%   $226.8821   $226.88   $226.90   $226.90  
  Purchase #2 $216.51   10.543%   $239.3366   $239.34   $239.35   $239.30  
  Purchase #3 $94.38   11.196%   $104.9468   $104.95   $104.95   $104.90  
  Purchase #4 $18.88   8.142%   $20.4172   $20.42   $20.40   $20.40  
  Purchase #5 $21.83   3.504%   $22.5949   $22.59   $22.60   $22.60  
  Purchase #6 $175.48   10.684%   $194.2283   $194.23   $194.25   $194.20  
  Purchase #7 $247.32   5.275%   $260.3661   $260.37   $260.35   $260.40  
  7 purchase totals = $978.09       $1,068.7720   $1,068.78   $1,068.80   $1,068.70