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 $232.35   12.329%   $260.9964   $261.00   $261.00   $261.00  
  Purchase #2 $117.95   10.523%   $130.3619   $130.36   $130.35   $130.40  
  Purchase #3 $71.75   12.771%   $80.9132   $80.91   $80.90   $80.90  
  Purchase #4 $169.93   4.435%   $177.4664   $177.47   $177.45   $177.50  
  Purchase #5 $121.55   6.630%   $129.6088   $129.61   $129.60   $129.60  
  Purchase #6 $60.76   9.504%   $66.5346   $66.53   $66.55   $66.50  
  Purchase #7 $185.32   4.857%   $194.321   $194.32   $194.30   $194.30  
  7 purchase totals = $959.61       $1,040.2023   $1,040.20   $1,040.15   $1,040.20