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 $60.79   5.113%   $63.8982   $63.90   $63.90   $63.90  
  Purchase #2 $55.35   4.711%   $57.9575   $57.96   $57.95   $58.00  
  Purchase #3 $137.51   9.807%   $150.9956   $151.00   $151.00   $151.00  
  Purchase #4 $161.66   3.853%   $167.8888   $167.89   $167.90   $167.90  
  Purchase #5 $109.83   3.334%   $113.4917   $113.49   $113.50   $113.50  
  Purchase #6 $134.47   10.294%   $148.3123   $148.31   $148.30   $148.30  
  Purchase #7 $108.76   12.177%   $122.0037   $122.00   $122.00   $122.00  
  7 purchase totals = $768.37       $824.5478   $824.55   $824.55   $824.60