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 $236.99   4.164%   $246.8583   $246.86   $246.85   $246.90  
  Purchase #2 $64.75   5.625%   $68.3922   $68.39   $68.40   $68.40  
  Purchase #3 $152.49   8.832%   $165.9579   $165.96   $165.95   $166.00  
  Purchase #4 $211.35   12.167%   $237.065   $237.07   $237.05   $237.10  
  Purchase #5 $40.97   8.329%   $44.3824   $44.38   $44.40   $44.40  
  Purchase #6 $94.45   11.550%   $105.359   $105.36   $105.35   $105.40  
  Purchase #7 $223.93   5.304%   $235.8072   $235.81   $235.80   $235.80  
  7 purchase totals = $1,024.93       $1,103.8220   $1,103.83   $1,103.80   $1,104.00