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 $250.73   5.817%   $265.315   $265.32   $265.30   $265.30  
  Purchase #2 $81.83   3.722%   $84.8757   $84.88   $84.90   $84.90  
  Purchase #3 $18.45   5.470%   $19.4592   $19.46   $19.45   $19.50  
  Purchase #4 $45.79   4.298%   $47.7581   $47.76   $47.75   $47.80  
  Purchase #5 $93.30   5.357%   $98.2981   $98.30   $98.30   $98.30  
  Purchase #6 $107.31   5.767%   $113.4986   $113.50   $113.50   $113.50  
  Purchase #7 $142.32   7.349%   $152.7791   $152.78   $152.80   $152.80  
  7 purchase totals = $739.73       $781.9838   $782.00   $782.00   $782.10