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 $63.83   13.614%   $72.5198   $72.52   $72.50   $72.50  
  Purchase #2 $249.61   12.571%   $280.9885   $280.99   $281.00   $281.00  
  Purchase #3 $74.54   10.663%   $82.4882   $82.49   $82.50   $82.50  
  Purchase #4 $248.98   11.681%   $278.0634   $278.06   $278.05   $278.10  
  Purchase #5 $214.25   7.516%   $230.353   $230.35   $230.35   $230.40  
  Purchase #6 $48.60   5.154%   $51.1048   $51.10   $51.10   $51.10  
  Purchase #7 $224.98   6.307%   $239.1695   $239.17   $239.15   $239.20  
  7 purchase totals = $1,124.79       $1,234.6872   $1,234.68   $1,234.65   $1,234.80