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 $104.91   13.658%   $119.2386   $119.24   $119.25   $119.20  
  Purchase #2 $136.94   9.349%   $149.7425   $149.74   $149.75   $149.70  
  Purchase #3 $245.69   8.460%   $266.4754   $266.48   $266.50   $266.50  
  Purchase #4 $95.85   11.151%   $106.5382   $106.54   $106.55   $106.50  
  Purchase #5 $22.32   6.628%   $23.7994   $23.80   $23.80   $23.80  
  Purchase #6 $104.44   13.313%   $118.3441   $118.34   $118.35   $118.30  
  Purchase #7 $81.26   8.784%   $88.3979   $88.40   $88.40   $88.40  
  7 purchase totals = $791.41       $872.5361   $872.54   $872.60   $872.40