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 $111.41   6.502%   $118.6539   $118.65   $118.65   $118.70  
  Purchase #2 $61.82   7.396%   $66.3922   $66.39   $66.40   $66.40  
  Purchase #3 $67.36   6.708%   $71.8785   $71.88   $71.90   $71.90  
  Purchase #4 $100.54   4.428%   $104.9919   $104.99   $105.00   $105.00  
  Purchase #5 $89.99   7.376%   $96.6277   $96.63   $96.65   $96.60  
  Purchase #6 $205.88   9.319%   $225.066   $225.07   $225.05   $225.10  
  Purchase #7 $112.80   6.521%   $120.1557   $120.16   $120.15   $120.20  
  7 purchase totals = $749.80       $803.7659   $803.77   $803.80   $803.90