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 $65.86   5.190%   $69.2781   $69.28   $69.30   $69.30  
  Purchase #2 $119.29   6.410%   $126.9365   $126.94   $126.95   $126.90  
  Purchase #3 $226.74   13.750%   $257.9168   $257.92   $257.90   $257.90  
  Purchase #4 $91.27   4.838%   $95.6856   $95.69   $95.70   $95.70  
  Purchase #5 $150.64   5.649%   $159.1497   $159.15   $159.15   $159.10  
  Purchase #6 $23.74   5.367%   $25.0141   $25.01   $25.00   $25.00  
  Purchase #7 $124.47   7.129%   $133.3435   $133.34   $133.35   $133.30  
  7 purchase totals = $802.01       $867.3243   $867.33   $867.35   $867.20