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 $116.73   8.323%   $126.4454   $126.45   $126.45   $126.40  
  Purchase #2 $201.68   12.295%   $226.4766   $226.48   $226.50   $226.50  
  Purchase #3 $86.42   3.588%   $89.5207   $89.52   $89.50   $89.50  
  Purchase #4 $31.63   11.382%   $35.2301   $35.23   $35.25   $35.20  
  Purchase #5 $197.29   13.680%   $224.2793   $224.28   $224.30   $224.30  
  Purchase #6 $194.57   12.375%   $218.648   $218.65   $218.65   $218.60  
  Purchase #7 $186.98   6.554%   $199.2347   $199.23   $199.25   $199.20  
  7 purchase totals = $1,015.30       $1,119.8348   $1,119.84   $1,119.90   $1,119.70