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 $59.34   10.568%   $65.6111   $65.61   $65.60   $65.60  
  Purchase #2 $61.38   3.113%   $63.2908   $63.29   $63.30   $63.30  
  Purchase #3 $12.50   4.844%   $13.1055   $13.11   $13.10   $13.10  
  Purchase #4 $218.80   6.292%   $232.5669   $232.57   $232.55   $232.60  
  Purchase #5 $182.87   10.387%   $201.8647   $201.86   $201.85   $201.90  
  Purchase #6 $65.27   10.523%   $72.1384   $72.14   $72.15   $72.10  
  Purchase #7 $182.97   4.574%   $191.339   $191.34   $191.35   $191.30  
  7 purchase totals = $783.13       $839.9164   $839.92   $839.90   $839.90