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 $218.76   10.265%   $241.2157   $241.22   $241.20   $241.20  
  Purchase #2 $99.35   3.624%   $102.9504   $102.95   $102.95   $103.00  
  Purchase #3 $216.99   5.611%   $229.1653   $229.17   $229.15   $229.20  
  Purchase #4 $246.41   6.696%   $262.9096   $262.91   $262.90   $262.90  
  Purchase #5 $127.27   3.609%   $131.8632   $131.86   $131.85   $131.90  
  Purchase #6 $7.29   10.289%   $8.0401   $8.04   $8.05   $8.00  
  Purchase #7 $74.61   6.201%   $79.2366   $79.24   $79.25   $79.20  
  7 purchase totals = $990.68       $1,055.3809   $1,055.39   $1,055.35   $1,055.40