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 $67.77   7.455%   $72.8223   $72.82   $72.80   $72.80  
  Purchase #2 $147.61   5.314%   $155.454   $155.45   $155.45   $155.50  
  Purchase #3 $170.69   8.594%   $185.3591   $185.36   $185.35   $185.40  
  Purchase #4 $66.76   4.429%   $69.7168   $69.72   $69.70   $69.70  
  Purchase #5 $72.42   5.684%   $76.5364   $76.54   $76.55   $76.50  
  Purchase #6 $235.31   9.227%   $257.0221   $257.02   $257.00   $257.00  
  Purchase #7 $126.39   7.604%   $136.0007   $136.00   $136.00   $136.00  
  7 purchase totals = $886.95       $952.9114   $952.91   $952.85   $952.90