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 $61.87   7.559%   $66.5468   $66.55   $66.55   $66.50  
  Purchase #2 $132.61   13.253%   $150.1848   $150.18   $150.20   $150.20  
  Purchase #3 $211.97   10.302%   $233.8071   $233.81   $233.80   $233.80  
  Purchase #4 $146.96   5.176%   $154.5666   $154.57   $154.55   $154.60  
  Purchase #5 $231.81   7.780%   $249.8448   $249.84   $249.85   $249.80  
  Purchase #6 $137.40   10.254%   $151.489   $151.49   $151.50   $151.50  
  Purchase #7 $179.43   4.108%   $186.801   $186.80   $186.80   $186.80  
  7 purchase totals = $1,102.05       $1,193.2401   $1,193.24   $1,193.25   $1,193.20