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 $67.95   9.763%   $74.584   $74.58   $74.60   $74.60  
  Purchase #2 $124.45   6.434%   $132.4571   $132.46   $132.45   $132.50  
  Purchase #3 $73.33   3.686%   $76.0329   $76.03   $76.05   $76.00  
  Purchase #4 $244.51   12.754%   $275.6948   $275.69   $275.70   $275.70  
  Purchase #5 $221.26   4.280%   $230.7299   $230.73   $230.75   $230.70  
  Purchase #6 $40.35   7.633%   $43.4299   $43.43   $43.45   $43.40  
  Purchase #7 $14.65   13.705%   $16.6578   $16.66   $16.65   $16.70  
  7 purchase totals = $786.50       $849.5864   $849.58   $849.65   $849.60