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 $66.48   10.809%   $73.6658   $73.67   $73.65   $73.70  
  Purchase #2 $124.92   13.509%   $141.7954   $141.80   $141.80   $141.80  
  Purchase #3 $15.89   5.176%   $16.7125   $16.71   $16.70   $16.70  
  Purchase #4 $249.64   10.459%   $275.7498   $275.75   $275.75   $275.70  
  Purchase #5 $11.42   9.456%   $12.4999   $12.50   $12.50   $12.50  
  Purchase #6 $52.56   11.806%   $58.7652   $58.77   $58.75   $58.80  
  Purchase #7 $163.66   7.794%   $176.4157   $176.42   $176.40   $176.40  
  7 purchase totals = $684.57       $755.6043   $755.62   $755.55   $755.60