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 $68.51   11.816%   $76.6051   $76.61   $76.60   $76.60  
  Purchase #2 $18.44   6.635%   $19.6635   $19.66   $19.65   $19.70  
  Purchase #3 $155.77   11.378%   $173.4935   $173.49   $173.50   $173.50  
  Purchase #4 $160.91   3.871%   $167.1388   $167.14   $167.15   $167.10  
  Purchase #5 $161.80   6.115%   $171.6941   $171.69   $171.70   $171.70  
  Purchase #6 $40.27   7.422%   $43.2588   $43.26   $43.25   $43.30  
  Purchase #7 $109.94   8.248%   $119.0079   $119.01   $119.00   $119.00  
  7 purchase totals = $715.64       $770.8617   $770.86   $770.85   $770.90