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 $244.42   13.257%   $276.8228   $276.82   $276.80   $276.80  
  Purchase #2 $87.82   9.352%   $96.0329   $96.03   $96.05   $96.00  
  Purchase #3 $76.44   3.431%   $79.0627   $79.06   $79.05   $79.10  
  Purchase #4 $76.31   3.809%   $79.2166   $79.22   $79.20   $79.20  
  Purchase #5 $150.75   4.555%   $157.6167   $157.62   $157.60   $157.60  
  Purchase #6 $119.93   5.778%   $126.8596   $126.86   $126.85   $126.90  
  Purchase #7 $44.82   6.767%   $47.853   $47.85   $47.85   $47.90  
  7 purchase totals = $800.49       $863.4643   $863.46   $863.40   $863.50