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 $232.56   12.208%   $260.9509   $260.95   $260.95   $261.00  
  Purchase #2 $216.47   10.580%   $239.3725   $239.37   $239.35   $239.40  
  Purchase #3 $37.76   12.798%   $42.5925   $42.59   $42.60   $42.60  
  Purchase #4 $228.66   13.404%   $259.3096   $259.31   $259.30   $259.30  
  Purchase #5 $107.27   12.198%   $120.3548   $120.35   $120.35   $120.40  
  Purchase #6 $41.29   5.554%   $43.5832   $43.58   $43.60   $43.60  
  Purchase #7 $121.83   7.370%   $130.8089   $130.81   $130.80   $130.80  
  7 purchase totals = $985.84       $1,096.9724   $1,096.96   $1,096.95   $1,097.10