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 $237.51   13.448%   $269.4503   $269.45   $269.45   $269.50  
  Purchase #2 $238.27   12.139%   $267.1936   $267.19   $267.20   $267.20  
  Purchase #3 $78.41   4.705%   $82.0992   $82.10   $82.10   $82.10  
  Purchase #4 $13.52   7.347%   $14.5133   $14.51   $14.50   $14.50  
  Purchase #5 $73.36   8.869%   $79.8663   $79.87   $79.85   $79.90  
  Purchase #6 $173.37   12.698%   $195.3845   $195.38   $195.40   $195.40  
  Purchase #7 $111.51   3.839%   $115.7909   $115.79   $115.80   $115.80  
  7 purchase totals = $925.95       $1,024.2981   $1,024.29   $1,024.30   $1,024.40