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 $62.30   3.475%   $64.4649   $64.46   $64.45   $64.50  
  Purchase #2 $238.73   11.285%   $265.6707   $265.67   $265.65   $265.70  
  Purchase #3 $83.26   11.102%   $92.5035   $92.50   $92.50   $92.50  
  Purchase #4 $154.70   9.295%   $169.0794   $169.08   $169.10   $169.10  
  Purchase #5 $40.93   6.769%   $43.7006   $43.70   $43.70   $43.70  
  Purchase #6 $9.93   8.636%   $10.7876   $10.79   $10.80   $10.80  
  Purchase #7 $169.69   9.837%   $186.3824   $186.38   $186.40   $186.40  
  7 purchase totals = $759.54       $832.5891   $832.58   $832.60   $832.70