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 $192.76   11.636%   $215.1896   $215.19   $215.20   $215.20  
  Purchase #2 $5.34   3.390%   $5.521   $5.52   $5.50   $5.50  
  Purchase #3 $116.81   7.390%   $125.4423   $125.44   $125.45   $125.40  
  Purchase #4 $73.39   3.235%   $75.7642   $75.76   $75.75   $75.80  
  Purchase #5 $236.68   5.833%   $250.4855   $250.49   $250.50   $250.50  
  Purchase #6 $126.43   4.796%   $132.4936   $132.49   $132.50   $132.50  
  Purchase #7 $188.67   10.788%   $209.0237   $209.02   $209.00   $209.00  
  7 purchase totals = $940.08       $1,013.9199   $1,013.91   $1,013.90   $1,013.90