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 $67.67   13.620%   $76.8867   $76.89   $76.90   $76.90  
  Purchase #2 $233.97   6.275%   $248.6516   $248.65   $248.65   $248.70  
  Purchase #3 $214.91   10.660%   $237.8194   $237.82   $237.80   $237.80  
  Purchase #4 $232.79   11.303%   $259.1023   $259.10   $259.10   $259.10  
  Purchase #5 $30.90   9.397%   $33.8037   $33.80   $33.80   $33.80  
  Purchase #6 $21.87   7.558%   $23.5229   $23.52   $23.50   $23.50  
  Purchase #7 $176.43   7.388%   $189.4646   $189.46   $189.45   $189.50  
  7 purchase totals = $978.54       $1,069.2512   $1,069.24   $1,069.20   $1,069.30