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 $76.98   11.623%   $85.9274   $85.93   $85.95   $85.90  
  Purchase #2 $136.29   9.874%   $149.7473   $149.75   $149.75   $149.70  
  Purchase #3 $143.53   11.757%   $160.4048   $160.40   $160.40   $160.40  
  Purchase #4 $34.94   4.350%   $36.4599   $36.46   $36.45   $36.50  
  Purchase #5 $86.86   9.446%   $95.0648   $95.06   $95.05   $95.10  
  Purchase #6 $195.72   8.369%   $212.0998   $212.10   $212.10   $212.10  
  Purchase #7 $99.37   10.610%   $109.9132   $109.91   $109.90   $109.90  
  7 purchase totals = $773.69       $849.6172   $849.61   $849.60   $849.60