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 $94.54   11.713%   $105.6135   $105.61   $105.60   $105.60  
  Purchase #2 $88.42   5.217%   $93.0329   $93.03   $93.05   $93.00  
  Purchase #3 $241.99   9.814%   $265.7389   $265.74   $265.75   $265.70  
  Purchase #4 $141.83   3.376%   $146.6182   $146.62   $146.60   $146.60  
  Purchase #5 $9.54   11.279%   $10.616   $10.62   $10.60   $10.60  
  Purchase #6 $126.34   5.244%   $132.9653   $132.97   $132.95   $133.00  
  Purchase #7 $112.59   10.176%   $124.0472   $124.05   $124.05   $124.00  
  7 purchase totals = $815.25       $878.6320   $878.64   $878.60   $878.50