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 $66.57   11.487%   $74.2169   $74.22   $74.20   $74.20  
  Purchase #2 $21.77   10.351%   $24.0234   $24.02   $24.00   $24.00  
  Purchase #3 $66.53   6.549%   $70.887   $70.89   $70.90   $70.90  
  Purchase #4 $60.36   3.217%   $62.3018   $62.30   $62.30   $62.30  
  Purchase #5 $123.38   10.791%   $136.6939   $136.69   $136.70   $136.70  
  Purchase #6 $222.37   11.511%   $247.967   $247.97   $247.95   $248.00  
  Purchase #7 $47.72   7.553%   $51.3243   $51.32   $51.30   $51.30  
  7 purchase totals = $608.70       $667.4143   $667.41   $667.35   $667.40