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 $86.40   11.461%   $96.3023   $96.30   $96.30   $96.30  
  Purchase #2 $130.28   6.850%   $139.2042   $139.20   $139.20   $139.20  
  Purchase #3 $68.76   13.690%   $78.1732   $78.17   $78.15   $78.20  
  Purchase #4 $200.30   12.872%   $226.0826   $226.08   $226.10   $226.10  
  Purchase #5 $99.92   8.729%   $108.642   $108.64   $108.65   $108.60  
  Purchase #6 $90.79   11.585%   $101.308   $101.31   $101.30   $101.30  
  Purchase #7 $175.90   13.397%   $199.4653   $199.47   $199.45   $199.50  
  7 purchase totals = $852.35       $949.1776   $949.17   $949.15   $949.20