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 $94.61   12.752%   $106.6747   $106.67   $106.65   $106.70  
  Purchase #2 $156.94   10.478%   $173.3842   $173.38   $173.40   $173.40  
  Purchase #3 $163.89   3.419%   $169.4934   $169.49   $169.50   $169.50  
  Purchase #4 $126.59   3.306%   $130.7751   $130.78   $130.80   $130.80  
  Purchase #5 $42.28   4.389%   $44.1357   $44.14   $44.15   $44.10  
  Purchase #6 $231.25   12.116%   $259.2683   $259.27   $259.25   $259.30  
  Purchase #7 $98.88   10.312%   $109.0765   $109.08   $109.10   $109.10  
  7 purchase totals = $914.44       $992.8079   $992.81   $992.85   $992.90