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 $135.98   11.749%   $151.9563   $151.96   $151.95   $152.00  
  Purchase #2 $5.51   12.532%   $6.2005   $6.20   $6.20   $6.20  
  Purchase #3 $245.93   11.629%   $274.5292   $274.53   $274.55   $274.50  
  Purchase #4 $89.26   13.573%   $101.3753   $101.38   $101.40   $101.40  
  Purchase #5 $128.80   10.611%   $142.467   $142.47   $142.45   $142.50  
  Purchase #6 $16.48   13.432%   $18.6936   $18.69   $18.70   $18.70  
  Purchase #7 $8.56   9.542%   $9.3768   $9.38   $9.40   $9.40  
  7 purchase totals = $630.52       $704.5987   $704.61   $704.65   $704.70