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 $105.71   13.238%   $119.7039   $119.70   $119.70   $119.70  
  Purchase #2 $111.38   13.548%   $126.4698   $126.47   $126.45   $126.50  
  Purchase #3 $14.73   8.379%   $15.9642   $15.96   $15.95   $16.00  
  Purchase #4 $197.88   5.464%   $208.6922   $208.69   $208.70   $208.70  
  Purchase #5 $10.93   3.598%   $11.3233   $11.32   $11.30   $11.30  
  Purchase #6 $228.52   3.217%   $235.8715   $235.87   $235.85   $235.90  
  Purchase #7 $185.75   12.344%   $208.679   $208.68   $208.70   $208.70  
  7 purchase totals = $854.90       $926.7039   $926.69   $926.65   $926.80