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 $92.85   5.391%   $97.8555   $97.86   $97.85   $97.90  
  Purchase #2 $159.96   3.731%   $165.9281   $165.93   $165.95   $165.90  
  Purchase #3 $87.30   4.637%   $91.3481   $91.35   $91.35   $91.30  
  Purchase #4 $218.25   4.547%   $228.1738   $228.17   $228.15   $228.20  
  Purchase #5 $14.63   5.667%   $15.4591   $15.46   $15.45   $15.50  
  Purchase #6 $15.88   5.561%   $16.7631   $16.76   $16.75   $16.80  
  Purchase #7 $47.25   8.709%   $51.365   $51.37   $51.35   $51.40  
  7 purchase totals = $636.12       $666.8927   $666.90   $666.85   $667.00