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 $68.61   9.227%   $74.9406   $74.94   $74.95   $74.90  
  Purchase #2 $194.53   9.700%   $213.3994   $213.40   $213.40   $213.40  
  Purchase #3 $117.76   6.149%   $125.0011   $125.00   $125.00   $125.00  
  Purchase #4 $220.94   13.553%   $250.884   $250.88   $250.90   $250.90  
  Purchase #5 $82.43   9.509%   $90.2683   $90.27   $90.25   $90.30  
  Purchase #6 $118.88   7.728%   $128.067   $128.07   $128.05   $128.10  
  Purchase #7 $33.50   12.677%   $37.7468   $37.75   $37.75   $37.70  
  7 purchase totals = $836.65       $920.3072   $920.31   $920.30   $920.30