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 $53.43   5.481%   $56.3585   $56.36   $56.35   $56.40  
  Purchase #2 $56.52   5.268%   $59.4975   $59.50   $59.50   $59.50  
  Purchase #3 $182.54   7.534%   $196.2926   $196.29   $196.30   $196.30  
  Purchase #4 $69.70   9.526%   $76.3396   $76.34   $76.35   $76.30  
  Purchase #5 $25.27   4.174%   $26.3248   $26.32   $26.30   $26.30  
  Purchase #6 $54.42   5.398%   $57.3576   $57.36   $57.35   $57.40  
  Purchase #7 $231.58   9.169%   $252.8136   $252.81   $252.80   $252.80  
  7 purchase totals = $673.46       $724.9842   $724.98   $724.95   $725.00