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 $171.79   7.148%   $184.0695   $184.07   $184.05   $184.10  
  Purchase #2 $173.83   9.260%   $189.9267   $189.93   $189.95   $189.90  
  Purchase #3 $62.45   11.671%   $69.7385   $69.74   $69.75   $69.70  
  Purchase #4 $194.74   5.741%   $205.92   $205.92   $205.90   $205.90  
  Purchase #5 $226.62   10.828%   $251.1584   $251.16   $251.15   $251.20  
  Purchase #6 $249.96   13.811%   $284.482   $284.48   $284.50   $284.50  
  Purchase #7 $218.91   13.274%   $247.9681   $247.97   $247.95   $248.00  
  7 purchase totals = $1,298.30       $1,433.2632   $1,433.27   $1,433.25   $1,433.30