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 $58.82   6.445%   $62.6109   $62.61   $62.60   $62.60  
  Purchase #2 $96.66   13.367%   $109.5805   $109.58   $109.60   $109.60  
  Purchase #3 $9.69   5.646%   $10.2371   $10.24   $10.25   $10.20  
  Purchase #4 $165.83   7.640%   $178.4994   $178.50   $178.50   $178.50  
  Purchase #5 $5.34   13.620%   $6.0673   $6.07   $6.05   $6.10  
  Purchase #6 $76.72   11.851%   $85.8121   $85.81   $85.80   $85.80  
  Purchase #7 $244.74   8.155%   $264.6985   $264.70   $264.70   $264.70  
  7 purchase totals = $657.80       $717.5058   $717.51   $717.50   $717.50