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 $148.62   12.421%   $167.0801   $167.08   $167.10   $167.10  
  Purchase #2 $72.98   5.305%   $76.8516   $76.85   $76.85   $76.90  
  Purchase #3 $74.73   8.323%   $80.9498   $80.95   $80.95   $80.90  
  Purchase #4 $233.38   12.583%   $262.7462   $262.75   $262.75   $262.70  
  Purchase #5 $136.84   12.697%   $154.2146   $154.21   $154.20   $154.20  
  Purchase #6 $151.48   3.201%   $156.3289   $156.33   $156.35   $156.30  
  Purchase #7 $16.62   9.462%   $18.1926   $18.19   $18.20   $18.20  
  7 purchase totals = $834.65       $916.3638   $916.36   $916.40   $916.30