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 $70.53   3.103%   $72.7185   $72.72   $72.70   $72.70  
  Purchase #2 $209.64   11.614%   $233.9876   $233.99   $234.00   $234.00  
  Purchase #3 $226.97   8.847%   $247.05   $247.05   $247.05   $247.10  
  Purchase #4 $213.68   13.631%   $242.8067   $242.81   $242.80   $242.80  
  Purchase #5 $229.93   13.434%   $260.8188   $260.82   $260.80   $260.80  
  Purchase #6 $94.40   7.143%   $101.143   $101.14   $101.15   $101.10  
  Purchase #7 $238.65   6.852%   $255.0023   $255.00   $255.00   $255.00  
  7 purchase totals = $1,283.80       $1,413.5269   $1,413.53   $1,413.50   $1,413.50