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 $58.39   3.205%   $60.2614   $60.26   $60.25   $60.30  
  Purchase #2 $182.59   10.386%   $201.5538   $201.55   $201.55   $201.60  
  Purchase #3 $247.55   6.535%   $263.7274   $263.73   $263.75   $263.70  
  Purchase #4 $68.51   3.578%   $70.9613   $70.96   $70.95   $71.00  
  Purchase #5 $105.65   10.466%   $116.7073   $116.71   $116.70   $116.70  
  Purchase #6 $103.82   12.657%   $116.9605   $116.96   $116.95   $117.00  
  Purchase #7 $28.96   5.582%   $30.5765   $30.58   $30.60   $30.60  
  7 purchase totals = $795.47       $860.7482   $860.75   $860.75   $860.90