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 $225.42   8.326%   $244.1885   $244.19   $244.20   $244.20  
  Purchase #2 $63.69   7.208%   $68.2808   $68.28   $68.30   $68.30  
  Purchase #3 $65.70   13.439%   $74.5294   $74.53   $74.55   $74.50  
  Purchase #4 $222.57   5.303%   $234.3729   $234.37   $234.35   $234.40  
  Purchase #5 $79.78   8.308%   $86.4081   $86.41   $86.40   $86.40  
  Purchase #6 $53.79   6.103%   $57.0728   $57.07   $57.05   $57.10  
  Purchase #7 $165.53   7.764%   $178.3817   $178.38   $178.40   $178.40  
  7 purchase totals = $876.48       $943.2342   $943.23   $943.25   $943.30