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 $91.27   12.323%   $102.5172   $102.52   $102.50   $102.50  
  Purchase #2 $96.98   4.861%   $101.6942   $101.69   $101.70   $101.70  
  Purchase #3 $123.97   5.798%   $131.1578   $131.16   $131.15   $131.20  
  Purchase #4 $67.93   6.351%   $72.2442   $72.24   $72.25   $72.20  
  Purchase #5 $179.60   7.440%   $192.9622   $192.96   $192.95   $193.00  
  Purchase #6 $85.55   10.147%   $94.2308   $94.23   $94.25   $94.20  
  Purchase #7 $236.76   8.643%   $257.2232   $257.22   $257.20   $257.20  
  7 purchase totals = $882.06       $952.0296   $952.02   $952.00   $952.00