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 $192.35   8.395%   $208.4978   $208.50   $208.50   $208.50  
  Purchase #2 $93.33   3.644%   $96.7309   $96.73   $96.75   $96.70  
  Purchase #3 $235.36   5.655%   $248.6696   $248.67   $248.65   $248.70  
  Purchase #4 $113.58   10.245%   $125.2163   $125.22   $125.20   $125.20  
  Purchase #5 $222.46   10.828%   $246.548   $246.55   $246.55   $246.50  
  Purchase #6 $99.78   11.361%   $111.116   $111.12   $111.10   $111.10  
  Purchase #7 $177.80   10.314%   $196.1383   $196.14   $196.15   $196.10  
  7 purchase totals = $1,134.66       $1,232.9169   $1,232.93   $1,232.90   $1,232.80