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 $223.73   10.231%   $246.6198   $246.62   $246.60   $246.60  
  Purchase #2 $149.59   4.461%   $156.2632   $156.26   $156.25   $156.30  
  Purchase #3 $48.60   6.471%   $51.7449   $51.74   $51.75   $51.70  
  Purchase #4 $117.64   5.152%   $123.7008   $123.70   $123.70   $123.70  
  Purchase #5 $241.84   11.847%   $270.4908   $270.49   $270.50   $270.50  
  Purchase #6 $57.26   12.511%   $64.4238   $64.42   $64.40   $64.40  
  Purchase #7 $12.89   11.559%   $14.38   $14.38   $14.40   $14.40  
  7 purchase totals = $851.55       $927.6233   $927.61   $927.60   $927.60