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 $47.95   5.714%   $50.6899   $50.69   $50.70   $50.70  
  Purchase #2 $152.96   8.425%   $165.8469   $165.85   $165.85   $165.80  
  Purchase #3 $52.78   10.415%   $58.277   $58.28   $58.30   $58.30  
  Purchase #4 $235.28   9.769%   $258.2645   $258.26   $258.25   $258.30  
  Purchase #5 $210.28   6.758%   $224.4907   $224.49   $224.50   $224.50  
  Purchase #6 $66.61   6.230%   $70.7598   $70.76   $70.75   $70.80  
  Purchase #7 $187.87   3.121%   $193.7334   $193.73   $193.75   $193.70  
  7 purchase totals = $953.73       $1,022.0622   $1,022.06   $1,022.10   $1,022.10