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 $193.98   5.868%   $205.3627   $205.36   $205.35   $205.40  
  Purchase #2 $233.83   6.869%   $249.8918   $249.89   $249.90   $249.90  
  Purchase #3 $147.51   11.201%   $164.0326   $164.03   $164.05   $164.00  
  Purchase #4 $235.26   12.751%   $265.258   $265.26   $265.25   $265.30  
  Purchase #5 $230.36   13.430%   $261.2973   $261.30   $261.30   $261.30  
  Purchase #6 $95.39   6.231%   $101.3338   $101.33   $101.35   $101.30  
  Purchase #7 $8.48   7.502%   $9.1162   $9.12   $9.10   $9.10  
  7 purchase totals = $1,144.81       $1,256.2924   $1,256.29   $1,256.30   $1,256.30