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 $188.99   13.153%   $213.8479   $213.85   $213.85   $213.80  
  Purchase #2 $229.28   5.138%   $241.0604   $241.06   $241.05   $241.10  
  Purchase #3 $55.26   4.329%   $57.6522   $57.65   $57.65   $57.70  
  Purchase #4 $126.54   4.644%   $132.4165   $132.42   $132.40   $132.40  
  Purchase #5 $202.65   8.522%   $219.9198   $219.92   $219.90   $219.90  
  Purchase #6 $5.65   4.312%   $5.8936   $5.89   $5.90   $5.90  
  Purchase #7 $111.87   5.493%   $118.015   $118.02   $118.00   $118.00  
  7 purchase totals = $920.24       $988.8054   $988.81   $988.75   $988.80