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 $196.75   9.796%   $216.0236   $216.02   $216.00   $216.00  
  Purchase #2 $80.60   11.820%   $90.1269   $90.13   $90.15   $90.10  
  Purchase #3 $21.56   10.506%   $23.8251   $23.83   $23.85   $23.80  
  Purchase #4 $243.92   5.519%   $257.3819   $257.38   $257.40   $257.40  
  Purchase #5 $238.37   3.832%   $247.5043   $247.50   $247.50   $247.50  
  Purchase #6 $239.70   5.377%   $252.5887   $252.59   $252.60   $252.60  
  Purchase #7 $219.89   11.338%   $244.8211   $244.82   $244.80   $244.80  
  7 purchase totals = $1,240.79       $1,332.2716   $1,332.27   $1,332.30   $1,332.20