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 $52.33   11.416%   $58.304   $58.30   $58.30   $58.30  
  Purchase #2 $223.92   6.799%   $239.1443   $239.14   $239.15   $239.10  
  Purchase #3 $212.64   10.301%   $234.544   $234.54   $234.55   $234.50  
  Purchase #4 $215.36   8.465%   $233.5902   $233.59   $233.60   $233.60  
  Purchase #5 $9.36   13.310%   $10.6058   $10.61   $10.60   $10.60  
  Purchase #6 $244.45   6.808%   $261.0922   $261.09   $261.10   $261.10  
  Purchase #7 $247.75   12.848%   $279.5809   $279.58   $279.60   $279.60  
  7 purchase totals = $1,205.81       $1,316.8614   $1,316.85   $1,316.90   $1,316.80