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 $49.63   6.196%   $52.7051   $52.71   $52.70   $52.70  
  Purchase #2 $51.64   9.317%   $56.4513   $56.45   $56.45   $56.50  
  Purchase #3 $233.39   9.683%   $255.9892   $255.99   $256.00   $256.00  
  Purchase #4 $219.61   11.764%   $245.4449   $245.44   $245.45   $245.40  
  Purchase #5 $132.67   7.770%   $142.9785   $142.98   $143.00   $143.00  
  Purchase #6 $193.43   6.349%   $205.7109   $205.71   $205.70   $205.70  
  Purchase #7 $82.86   4.300%   $86.423   $86.42   $86.40   $86.40  
  7 purchase totals = $963.23       $1,045.7029   $1,045.70   $1,045.70   $1,045.70