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 $80.99   8.617%   $87.9689   $87.97   $87.95   $88.00  
  Purchase #2 $86.47   11.492%   $96.4071   $96.41   $96.40   $96.40  
  Purchase #3 $117.51   7.758%   $126.6264   $126.63   $126.65   $126.60  
  Purchase #4 $231.89   5.195%   $243.9367   $243.94   $243.95   $243.90  
  Purchase #5 $12.56   13.458%   $14.2503   $14.25   $14.25   $14.30  
  Purchase #6 $96.42   8.155%   $104.2831   $104.28   $104.30   $104.30  
  Purchase #7 $119.79   6.423%   $127.4841   $127.48   $127.50   $127.50  
  7 purchase totals = $745.63       $800.9566   $800.96   $801.00   $801.00