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 $68.98   10.155%   $75.9849   $75.98   $76.00   $76.00  
  Purchase #2 $84.36   11.457%   $94.0251   $94.03   $94.05   $94.00  
  Purchase #3 $147.80   7.506%   $158.8939   $158.89   $158.90   $158.90  
  Purchase #4 $207.92   13.334%   $235.6441   $235.64   $235.65   $235.60  
  Purchase #5 $223.91   7.543%   $240.7995   $240.80   $240.80   $240.80  
  Purchase #6 $200.76   4.710%   $210.2158   $210.22   $210.20   $210.20  
  Purchase #7 $237.88   10.766%   $263.4902   $263.49   $263.50   $263.50  
  7 purchase totals = $1,171.61       $1,279.0535   $1,279.05   $1,279.10   $1,279.00