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 $108.76   9.376%   $118.9573   $118.96   $118.95   $119.00  
  Purchase #2 $168.35   6.829%   $179.8466   $179.85   $179.85   $179.80  
  Purchase #3 $61.85   5.692%   $65.3705   $65.37   $65.35   $65.40  
  Purchase #4 $107.61   6.332%   $114.4239   $114.42   $114.40   $114.40  
  Purchase #5 $226.80   11.328%   $252.4919   $252.49   $252.50   $252.50  
  Purchase #6 $12.45   13.258%   $14.1006   $14.10   $14.10   $14.10  
  Purchase #7 $102.48   13.808%   $116.6304   $116.63   $116.65   $116.60  
  7 purchase totals = $788.30       $861.8212   $861.82   $861.80   $861.80