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 $194.72   11.104%   $216.3417   $216.34   $216.35   $216.30  
  Purchase #2 $55.93   10.260%   $61.6684   $61.67   $61.65   $61.70  
  Purchase #3 $115.87   12.318%   $130.1429   $130.14   $130.15   $130.10  
  Purchase #4 $241.45   7.372%   $259.2497   $259.25   $259.25   $259.20  
  Purchase #5 $90.58   7.803%   $97.648   $97.65   $97.65   $97.60  
  Purchase #6 $170.85   4.432%   $178.4221   $178.42   $178.40   $178.40  
  Purchase #7 $73.68   5.864%   $78.0006   $78.00   $78.00   $78.00  
  7 purchase totals = $943.08       $1,021.4734   $1,021.47   $1,021.45   $1,021.30