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 $58.79   8.458%   $63.7625   $63.76   $63.75   $63.80  
  Purchase #2 $111.62   6.480%   $118.853   $118.85   $118.85   $118.90  
  Purchase #3 $117.39   4.795%   $123.0189   $123.02   $123.00   $123.00  
  Purchase #4 $7.87   7.834%   $8.4865   $8.49   $8.50   $8.50  
  Purchase #5 $100.70   7.473%   $108.2253   $108.23   $108.25   $108.20  
  Purchase #6 $241.90   6.614%   $257.8993   $257.90   $257.90   $257.90  
  Purchase #7 $89.64   9.309%   $97.9846   $97.98   $98.00   $98.00  
  7 purchase totals = $727.91       $778.2301   $778.23   $778.25   $778.30