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 $238.46   3.339%   $246.4222   $246.42   $246.40   $246.40  
  Purchase #2 $97.84   6.217%   $103.9227   $103.92   $103.90   $103.90  
  Purchase #3 $44.28   4.188%   $46.1344   $46.13   $46.15   $46.10  
  Purchase #4 $7.81   13.645%   $8.8757   $8.88   $8.90   $8.90  
  Purchase #5 $172.79   11.651%   $192.9218   $192.92   $192.90   $192.90  
  Purchase #6 $227.69   7.547%   $244.8738   $244.87   $244.85   $244.90  
  Purchase #7 $204.87   9.374%   $224.0745   $224.07   $224.05   $224.10  
  7 purchase totals = $993.74       $1,067.2251   $1,067.21   $1,067.15   $1,067.20