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 $23.74   11.633%   $26.5017   $26.50   $26.50   $26.50  
  Purchase #2 $9.52   10.572%   $10.5265   $10.53   $10.55   $10.50  
  Purchase #3 $127.31   11.305%   $141.7024   $141.70   $141.70   $141.70  
  Purchase #4 $228.49   6.771%   $243.9611   $243.96   $243.95   $244.00  
  Purchase #5 $206.67   11.251%   $229.9224   $229.92   $229.90   $229.90  
  Purchase #6 $87.59   8.317%   $94.8749   $94.87   $94.85   $94.90  
  Purchase #7 $206.54   4.535%   $215.9066   $215.91   $215.90   $215.90  
  7 purchase totals = $889.86       $963.3956   $963.39   $963.35   $963.40