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 $178.48   9.802%   $195.9746   $195.97   $195.95   $196.00  
  Purchase #2 $152.49   12.165%   $171.0404   $171.04   $171.05   $171.00  
  Purchase #3 $12.83   5.107%   $13.4852   $13.49   $13.50   $13.50  
  Purchase #4 $206.29   8.146%   $223.0944   $223.09   $223.10   $223.10  
  Purchase #5 $33.85   11.234%   $37.6527   $37.65   $37.65   $37.70  
  Purchase #6 $236.34   3.675%   $245.0255   $245.03   $245.05   $245.00  
  Purchase #7 $77.65   11.107%   $86.2746   $86.27   $86.25   $86.30  
  7 purchase totals = $897.93       $972.5474   $972.54   $972.55   $972.60