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 $20.43   7.381%   $21.9379   $21.94   $21.95   $21.90  
  Purchase #2 $7.48   3.776%   $7.7624   $7.76   $7.75   $7.80  
  Purchase #3 $108.46   6.276%   $115.2669   $115.27   $115.25   $115.30  
  Purchase #4 $230.58   6.736%   $246.1119   $246.11   $246.10   $246.10  
  Purchase #5 $56.74   10.264%   $62.5638   $62.56   $62.55   $62.60  
  Purchase #6 $202.77   6.404%   $215.7554   $215.76   $215.75   $215.80  
  Purchase #7 $250.47   7.360%   $268.9046   $268.90   $268.90   $268.90  
  7 purchase totals = $876.93       $938.3029   $938.30   $938.25   $938.40