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 $98.26   6.816%   $104.9574   $104.96   $104.95   $105.00  
  Purchase #2 $136.86   12.159%   $153.5008   $153.50   $153.50   $153.50  
  Purchase #3 $93.72   4.170%   $97.6281   $97.63   $97.65   $97.60  
  Purchase #4 $244.39   6.473%   $260.2094   $260.21   $260.20   $260.20  
  Purchase #5 $175.97   5.818%   $186.2079   $186.21   $186.20   $186.20  
  Purchase #6 $114.92   9.606%   $125.9592   $125.96   $125.95   $126.00  
  Purchase #7 $57.66   8.777%   $62.7208   $62.72   $62.70   $62.70  
  7 purchase totals = $921.78       $991.1836   $991.19   $991.15   $991.20