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 $53.94   10.441%   $59.5719   $59.57   $59.55   $59.60  
  Purchase #2 $234.99   12.785%   $265.0335   $265.03   $265.05   $265.00  
  Purchase #3 $115.26   9.565%   $126.2846   $126.28   $126.30   $126.30  
  Purchase #4 $129.70   13.490%   $147.1965   $147.20   $147.20   $147.20  
  Purchase #5 $76.43   13.694%   $86.8963   $86.90   $86.90   $86.90  
  Purchase #6 $151.38   10.706%   $167.5867   $167.59   $167.60   $167.60  
  Purchase #7 $240.78   8.714%   $261.7616   $261.76   $261.75   $261.80  
  7 purchase totals = $1,002.48       $1,114.3311   $1,114.33   $1,114.35   $1,114.40