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 $60.40   8.759%   $65.6904   $65.69   $65.70   $65.70  
  Purchase #2 $168.30   10.734%   $186.3653   $186.37   $186.35   $186.40  
  Purchase #3 $228.27   7.207%   $244.7214   $244.72   $244.70   $244.70  
  Purchase #4 $172.85   5.475%   $182.3135   $182.31   $182.30   $182.30  
  Purchase #5 $213.74   5.469%   $225.4294   $225.43   $225.45   $225.40  
  Purchase #6 $17.38   3.110%   $17.9205   $17.92   $17.90   $17.90  
  Purchase #7 $10.59   5.234%   $11.1443   $11.14   $11.15   $11.10  
  7 purchase totals = $871.53       $933.5848   $933.58   $933.55   $933.50