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 $67.33   13.419%   $76.365   $76.37   $76.35   $76.40  
  Purchase #2 $69.77   11.229%   $77.6045   $77.60   $77.60   $77.60  
  Purchase #3 $87.49   4.376%   $91.3186   $91.32   $91.30   $91.30  
  Purchase #4 $124.89   4.633%   $130.6762   $130.68   $130.70   $130.70  
  Purchase #5 $165.47   12.285%   $185.798   $185.80   $185.80   $185.80  
  Purchase #6 $157.35   8.197%   $170.248   $170.25   $170.25   $170.20  
  Purchase #7 $23.97   5.766%   $25.3521   $25.35   $25.35   $25.40  
  7 purchase totals = $696.27       $757.3624   $757.37   $757.35   $757.40