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 $68.82   8.771%   $74.8562   $74.86   $74.85   $74.90  
  Purchase #2 $26.38   3.497%   $27.3025   $27.30   $27.30   $27.30  
  Purchase #3 $121.83   8.217%   $131.8408   $131.84   $131.85   $131.80  
  Purchase #4 $112.40   4.446%   $117.3973   $117.40   $117.40   $117.40  
  Purchase #5 $168.83   4.579%   $176.5607   $176.56   $176.55   $176.60  
  Purchase #6 $157.81   9.444%   $172.7136   $172.71   $172.70   $172.70  
  Purchase #7 $65.32   5.549%   $68.9446   $68.94   $68.95   $68.90  
  7 purchase totals = $721.39       $769.6157   $769.61   $769.60   $769.60