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 $74.92   13.116%   $84.7465   $84.75   $84.75   $84.70  
  Purchase #2 $87.27   4.151%   $90.8926   $90.89   $90.90   $90.90  
  Purchase #3 $51.78   7.495%   $55.6609   $55.66   $55.65   $55.70  
  Purchase #4 $227.80   8.445%   $247.0377   $247.04   $247.05   $247.00  
  Purchase #5 $209.46   5.796%   $221.6003   $221.60   $221.60   $221.60  
  Purchase #6 $236.38   4.811%   $247.7522   $247.75   $247.75   $247.80  
  Purchase #7 $106.69   7.536%   $114.7302   $114.73   $114.75   $114.70  
  7 purchase totals = $994.30       $1,062.4204   $1,062.42   $1,062.45   $1,062.40