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 $10.26   11.165%   $11.4055   $11.41   $11.40   $11.40  
  Purchase #2 $9.69   10.164%   $10.6749   $10.67   $10.65   $10.70  
  Purchase #3 $24.81   8.578%   $26.9382   $26.94   $26.95   $26.90  
  Purchase #4 $96.54   3.339%   $99.7635   $99.76   $99.75   $99.80  
  Purchase #5 $126.30   6.572%   $134.6004   $134.60   $134.60   $134.60  
  Purchase #6 $131.76   11.191%   $146.5053   $146.51   $146.50   $146.50  
  Purchase #7 $157.42   12.246%   $176.6977   $176.70   $176.70   $176.70  
  7 purchase totals = $556.78       $606.5855   $606.59   $606.55   $606.60