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 $186.64   7.758%   $201.1195   $201.12   $201.10   $201.10  
  Purchase #2 $35.67   11.531%   $39.7831   $39.78   $39.80   $39.80  
  Purchase #3 $172.35   3.226%   $177.91   $177.91   $177.90   $177.90  
  Purchase #4 $168.92   12.191%   $189.513   $189.51   $189.50   $189.50  
  Purchase #5 $169.38   8.675%   $184.0737   $184.07   $184.05   $184.10  
  Purchase #6 $213.45   3.457%   $220.829   $220.83   $220.85   $220.80  
  Purchase #7 $6.49   3.305%   $6.7045   $6.70   $6.70   $6.70  
  7 purchase totals = $952.90       $1,019.9328   $1,019.92   $1,019.90   $1,019.90