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 $54.44   7.691%   $58.627   $58.63   $58.65   $58.60  
  Purchase #2 $152.25   13.791%   $173.2468   $173.25   $173.25   $173.20  
  Purchase #3 $64.66   13.625%   $73.4699   $73.47   $73.45   $73.50  
  Purchase #4 $86.96   9.638%   $95.3412   $95.34   $95.35   $95.30  
  Purchase #5 $164.76   5.357%   $173.5862   $173.59   $173.60   $173.60  
  Purchase #6 $226.66   11.169%   $251.9757   $251.98   $252.00   $252.00  
  Purchase #7 $231.29   13.847%   $263.3167   $263.32   $263.30   $263.30  
  7 purchase totals = $981.02       $1,089.5635   $1,089.58   $1,089.60   $1,089.50