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 $161.72   13.696%   $183.8692   $183.87   $183.85   $183.90  
  Purchase #2 $215.69   13.822%   $245.5027   $245.50   $245.50   $245.50  
  Purchase #3 $9.92   7.556%   $10.6696   $10.67   $10.65   $10.70  
  Purchase #4 $151.86   10.707%   $168.1197   $168.12   $168.10   $168.10  
  Purchase #5 $234.94   13.432%   $266.4971   $266.50   $266.50   $266.50  
  Purchase #6 $217.46   13.476%   $246.7649   $246.76   $246.75   $246.80  
  Purchase #7 $70.58   5.235%   $74.2749   $74.27   $74.25   $74.30  
  7 purchase totals = $1,062.17       $1,195.6981   $1,195.69   $1,195.60   $1,195.80