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 $22.60   10.206%   $24.9066   $24.91   $24.90   $24.90  
  Purchase #2 $32.29   10.443%   $35.662   $35.66   $35.65   $35.70  
  Purchase #3 $166.55   9.631%   $182.5904   $182.59   $182.60   $182.60  
  Purchase #4 $34.72   3.426%   $35.9095   $35.91   $35.90   $35.90  
  Purchase #5 $233.99   4.440%   $244.3792   $244.38   $244.40   $244.40  
  Purchase #6 $249.99   13.373%   $283.4212   $283.42   $283.40   $283.40  
  Purchase #7 $224.64   6.283%   $238.7541   $238.75   $238.75   $238.80  
  7 purchase totals = $964.78       $1,045.6230   $1,045.62   $1,045.60   $1,045.70