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 $67.40   13.253%   $76.3325   $76.33   $76.35   $76.30  
  Purchase #2 $86.25   8.555%   $93.6287   $93.63   $93.65   $93.60  
  Purchase #3 $123.66   10.767%   $136.9745   $136.97   $136.95   $137.00  
  Purchase #4 $206.34   13.274%   $233.7296   $233.73   $233.75   $233.70  
  Purchase #5 $8.88   13.122%   $10.0452   $10.05   $10.05   $10.00  
  Purchase #6 $43.87   9.758%   $48.1508   $48.15   $48.15   $48.20  
  Purchase #7 $213.70   4.810%   $223.979   $223.98   $224.00   $224.00  
  7 purchase totals = $750.10       $822.8403   $822.84   $822.90   $822.80