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 $46.57   12.475%   $52.3796   $52.38   $52.40   $52.40  
  Purchase #2 $213.87   8.771%   $232.6285   $232.63   $232.65   $232.60  
  Purchase #3 $247.27   8.649%   $268.6564   $268.66   $268.65   $268.70  
  Purchase #4 $74.26   11.246%   $82.6113   $82.61   $82.60   $82.60  
  Purchase #5 $74.80   9.470%   $81.8836   $81.88   $81.90   $81.90  
  Purchase #6 $61.80   5.136%   $64.974   $64.97   $64.95   $65.00  
  Purchase #7 $176.37   12.329%   $198.1147   $198.11   $198.10   $198.10  
  7 purchase totals = $894.94       $981.2481   $981.24   $981.25   $981.30