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 $62.96   6.813%   $67.2495   $67.25   $67.25   $67.20  
  Purchase #2 $185.40   3.759%   $192.3692   $192.37   $192.35   $192.40  
  Purchase #3 $106.57   6.402%   $113.3926   $113.39   $113.40   $113.40  
  Purchase #4 $71.95   7.854%   $77.601   $77.60   $77.60   $77.60  
  Purchase #5 $91.96   7.632%   $98.9784   $98.98   $99.00   $99.00  
  Purchase #6 $239.32   11.225%   $266.1837   $266.18   $266.20   $266.20  
  Purchase #7 $145.33   8.554%   $157.7615   $157.76   $157.75   $157.80  
  7 purchase totals = $903.49       $973.5359   $973.53   $973.55   $973.60