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 $151.30   6.345%   $160.9   $160.90   $160.90   $160.90  
  Purchase #2 $57.68   13.274%   $65.3364   $65.34   $65.35   $65.30  
  Purchase #3 $32.35   10.141%   $35.6306   $35.63   $35.65   $35.60  
  Purchase #4 $231.87   5.212%   $243.9551   $243.96   $243.95   $244.00  
  Purchase #5 $65.39   3.161%   $67.457   $67.46   $67.45   $67.50  
  Purchase #6 $65.91   7.858%   $71.0892   $71.09   $71.10   $71.10  
  Purchase #7 $240.67   13.123%   $272.2531   $272.25   $272.25   $272.30  
  7 purchase totals = $845.17       $916.6214   $916.63   $916.65   $916.70