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 $231.79   5.232%   $243.9173   $243.92   $243.90   $243.90  
  Purchase #2 $110.90   10.199%   $122.2107   $122.21   $122.20   $122.20  
  Purchase #3 $18.65   11.299%   $20.7573   $20.76   $20.75   $20.80  
  Purchase #4 $122.93   11.307%   $136.8297   $136.83   $136.85   $136.80  
  Purchase #5 $139.73   11.775%   $156.1832   $156.18   $156.20   $156.20  
  Purchase #6 $109.73   13.186%   $124.199   $124.20   $124.20   $124.20  
  Purchase #7 $145.58   11.233%   $161.933   $161.93   $161.95   $161.90  
  7 purchase totals = $879.31       $966.0302   $966.03   $966.05   $966.00