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 $244.49   6.822%   $261.1691   $261.17   $261.15   $261.20  
  Purchase #2 $177.26   11.365%   $197.4056   $197.41   $197.40   $197.40  
  Purchase #3 $180.27   3.316%   $186.2478   $186.25   $186.25   $186.20  
  Purchase #4 $66.79   6.443%   $71.0933   $71.09   $71.10   $71.10  
  Purchase #5 $33.51   5.871%   $35.4774   $35.48   $35.50   $35.50  
  Purchase #6 $141.55   9.618%   $155.1643   $155.16   $155.15   $155.20  
  Purchase #7 $160.58   13.230%   $181.8247   $181.82   $181.80   $181.80  
  7 purchase totals = $1,004.45       $1,088.3822   $1,088.38   $1,088.35   $1,088.40