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 $84.74   13.661%   $96.3163   $96.32   $96.30   $96.30  
  Purchase #2 $76.48   4.554%   $79.9629   $79.96   $79.95   $80.00  
  Purchase #3 $59.32   5.565%   $62.6212   $62.62   $62.60   $62.60  
  Purchase #4 $179.48   12.397%   $201.7301   $201.73   $201.75   $201.70  
  Purchase #5 $100.35   6.483%   $106.8557   $106.86   $106.85   $106.90  
  Purchase #6 $211.39   5.664%   $223.3631   $223.36   $223.35   $223.40  
  Purchase #7 $85.87   12.687%   $96.7643   $96.76   $96.75   $96.80  
  7 purchase totals = $797.63       $867.6136   $867.61   $867.55   $867.70