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 $66.31   4.410%   $69.2343   $69.23   $69.25   $69.20  
  Purchase #2 $236.81   13.566%   $268.9356   $268.94   $268.95   $268.90  
  Purchase #3 $69.25   6.563%   $73.7949   $73.79   $73.80   $73.80  
  Purchase #4 $176.67   6.181%   $187.59   $187.59   $187.60   $187.60  
  Purchase #5 $77.81   8.297%   $84.2659   $84.27   $84.25   $84.30  
  Purchase #6 $119.28   4.334%   $124.4496   $124.45   $124.45   $124.40  
  Purchase #7 $101.62   7.423%   $109.1633   $109.16   $109.15   $109.20  
  7 purchase totals = $847.75       $917.4336   $917.43   $917.45   $917.40