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 $65.93   11.184%   $73.3036   $73.30   $73.30   $73.30  
  Purchase #2 $119.28   10.697%   $132.0394   $132.04   $132.05   $132.00  
  Purchase #3 $55.68   10.272%   $61.3994   $61.40   $61.40   $61.40  
  Purchase #4 $218.88   12.247%   $245.6862   $245.69   $245.70   $245.70  
  Purchase #5 $129.70   10.530%   $143.3574   $143.36   $143.35   $143.40  
  Purchase #6 $52.90   10.685%   $58.5524   $58.55   $58.55   $58.60  
  Purchase #7 $226.32   6.452%   $240.9222   $240.92   $240.90   $240.90  
  7 purchase totals = $868.69       $955.2606   $955.26   $955.25   $955.30