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 $233.86   8.646%   $254.0795   $254.08   $254.10   $254.10  
  Purchase #2 $244.98   7.105%   $262.3858   $262.39   $262.40   $262.40  
  Purchase #3 $19.53   9.202%   $21.3272   $21.33   $21.35   $21.30  
  Purchase #4 $213.89   4.798%   $224.1524   $224.15   $224.15   $224.20  
  Purchase #5 $168.73   13.585%   $191.652   $191.65   $191.65   $191.70  
  Purchase #6 $28.35   11.701%   $31.6672   $31.67   $31.65   $31.70  
  Purchase #7 $130.97   6.103%   $138.9631   $138.96   $138.95   $139.00  
  7 purchase totals = $1,040.31       $1,124.2272   $1,124.23   $1,124.25   $1,124.40