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 $167.33   11.715%   $186.9327   $186.93   $186.95   $186.90  
  Purchase #2 $53.83   5.558%   $56.8219   $56.82   $56.80   $56.80  
  Purchase #3 $172.51   3.306%   $178.2132   $178.21   $178.20   $178.20  
  Purchase #4 $95.48   6.493%   $101.6795   $101.68   $101.70   $101.70  
  Purchase #5 $248.94   7.116%   $266.6546   $266.65   $266.65   $266.70  
  Purchase #6 $244.53   13.259%   $276.9522   $276.95   $276.95   $277.00  
  Purchase #7 $8.73   4.795%   $9.1486   $9.15   $9.15   $9.10  
  7 purchase totals = $991.35       $1,076.4027   $1,076.39   $1,076.40   $1,076.40