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 $95.86   3.140%   $98.87   $98.87   $98.85   $98.90  
  Purchase #2 $129.95   9.687%   $142.5383   $142.54   $142.55   $142.50  
  Purchase #3 $109.39   3.636%   $113.3674   $113.37   $113.35   $113.40  
  Purchase #4 $112.90   3.615%   $116.9813   $116.98   $117.00   $117.00  
  Purchase #5 $95.68   13.320%   $108.4246   $108.42   $108.40   $108.40  
  Purchase #6 $126.55   4.668%   $132.4574   $132.46   $132.45   $132.50  
  Purchase #7 $130.50   13.211%   $147.7404   $147.74   $147.75   $147.70  
  7 purchase totals = $800.83       $860.3794   $860.38   $860.35   $860.40