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 $54.66   7.357%   $58.6813   $58.68   $58.70   $58.70  
  Purchase #2 $89.38   7.376%   $95.9727   $95.97   $95.95   $96.00  
  Purchase #3 $87.75   3.181%   $90.5413   $90.54   $90.55   $90.50  
  Purchase #4 $53.65   5.538%   $56.6211   $56.62   $56.60   $56.60  
  Purchase #5 $215.53   11.310%   $239.9064   $239.91   $239.90   $239.90  
  Purchase #6 $205.97   3.756%   $213.7062   $213.71   $213.70   $213.70  
  Purchase #7 $192.85   9.838%   $211.8226   $211.82   $211.80   $211.80  
  7 purchase totals = $899.79       $967.2516   $967.25   $967.20   $967.20