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 $74.49   12.241%   $83.6083   $83.61   $83.60   $83.60  
  Purchase #2 $216.55   4.375%   $226.0241   $226.02   $226.00   $226.00  
  Purchase #3 $14.74   8.874%   $16.048   $16.05   $16.05   $16.00  
  Purchase #4 $166.62   4.456%   $174.0446   $174.04   $174.05   $174.00  
  Purchase #5 $250.96   4.142%   $261.3548   $261.35   $261.35   $261.40  
  Purchase #6 $117.32   11.582%   $130.908   $130.91   $130.90   $130.90  
  Purchase #7 $122.57   6.264%   $130.2478   $130.25   $130.25   $130.20  
  7 purchase totals = $963.25       $1,022.2356   $1,022.23   $1,022.20   $1,022.10