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 $119.74   13.670%   $136.1085   $136.11   $136.10   $136.10  
  Purchase #2 $178.25   10.479%   $196.9288   $196.93   $196.95   $196.90  
  Purchase #3 $10.35   12.305%   $11.6236   $11.62   $11.60   $11.60  
  Purchase #4 $86.94   11.373%   $96.8277   $96.83   $96.85   $96.80  
  Purchase #5 $121.51   3.676%   $125.9767   $125.98   $126.00   $126.00  
  Purchase #6 $181.99   7.616%   $195.8504   $195.85   $195.85   $195.90  
  Purchase #7 $17.61   9.481%   $19.2796   $19.28   $19.30   $19.30  
  7 purchase totals = $716.39       $782.5953   $782.60   $782.65   $782.60