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 $246.74   13.152%   $279.1912   $279.19   $279.20   $279.20  
  Purchase #2 $153.98   4.862%   $161.4665   $161.47   $161.45   $161.50  
  Purchase #3 $220.92   11.225%   $245.7183   $245.72   $245.70   $245.70  
  Purchase #4 $219.89   6.837%   $234.9239   $234.92   $234.90   $234.90  
  Purchase #5 $45.43   3.706%   $47.1136   $47.11   $47.10   $47.10  
  Purchase #6 $172.73   7.423%   $185.5517   $185.55   $185.55   $185.60  
  Purchase #7 $135.39   5.298%   $142.563   $142.56   $142.55   $142.60  
  7 purchase totals = $1,195.08       $1,296.5282   $1,296.52   $1,296.45   $1,296.60