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 $241.35   8.416%   $261.662   $261.66   $261.65   $261.70  
  Purchase #2 $13.71   8.337%   $14.853   $14.85   $14.85   $14.90  
  Purchase #3 $72.67   3.659%   $75.329   $75.33   $75.35   $75.30  
  Purchase #4 $249.52   6.324%   $265.2996   $265.30   $265.30   $265.30  
  Purchase #5 $156.93   7.571%   $168.8112   $168.81   $168.80   $168.80  
  Purchase #6 $223.40   4.213%   $232.8118   $232.81   $232.80   $232.80  
  Purchase #7 $171.83   10.559%   $189.9735   $189.97   $189.95   $190.00  
  7 purchase totals = $1,129.41       $1,208.7401   $1,208.73   $1,208.70   $1,208.80