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 $71.87   6.546%   $76.5746   $76.57   $76.55   $76.60  
  Purchase #2 $126.43   11.793%   $141.3399   $141.34   $141.35   $141.30  
  Purchase #3 $221.69   12.169%   $248.6675   $248.67   $248.65   $248.70  
  Purchase #4 $152.26   7.647%   $163.9033   $163.90   $163.90   $163.90  
  Purchase #5 $85.31   7.440%   $91.6571   $91.66   $91.65   $91.70  
  Purchase #6 $165.82   10.738%   $183.6258   $183.63   $183.65   $183.60  
  Purchase #7 $166.60   5.600%   $175.9296   $175.93   $175.95   $175.90  
  7 purchase totals = $989.98       $1,081.6978   $1,081.70   $1,081.70   $1,081.70