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 $87.43   12.481%   $98.3421   $98.34   $98.35   $98.30  
  Purchase #2 $193.86   7.832%   $209.0431   $209.04   $209.05   $209.00  
  Purchase #3 $44.63   9.454%   $48.8493   $48.85   $48.85   $48.80  
  Purchase #4 $243.55   3.670%   $252.4883   $252.49   $252.50   $252.50  
  Purchase #5 $60.70   8.771%   $66.024   $66.02   $66.00   $66.00  
  Purchase #6 $42.27   11.346%   $47.066   $47.07   $47.05   $47.10  
  Purchase #7 $164.48   6.294%   $174.8324   $174.83   $174.85   $174.80  
  7 purchase totals = $836.92       $896.6452   $896.64   $896.65   $896.50