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 $58.74   6.609%   $62.6221   $62.62   $62.60   $62.60  
  Purchase #2 $187.25   3.873%   $194.5022   $194.50   $194.50   $194.50  
  Purchase #3 $105.63   11.487%   $117.7637   $117.76   $117.75   $117.80  
  Purchase #4 $160.97   6.492%   $171.4202   $171.42   $171.40   $171.40  
  Purchase #5 $70.92   11.373%   $78.9857   $78.99   $79.00   $79.00  
  Purchase #6 $204.84   6.526%   $218.2079   $218.21   $218.20   $218.20  
  Purchase #7 $119.87   13.116%   $135.5921   $135.59   $135.60   $135.60  
  7 purchase totals = $908.22       $979.0939   $979.09   $979.05   $979.10