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 $156.96   13.757%   $178.553   $178.55   $178.55   $178.60  
  Purchase #2 $85.37   11.460%   $95.1534   $95.15   $95.15   $95.20  
  Purchase #3 $61.41   8.349%   $66.5371   $66.54   $66.55   $66.50  
  Purchase #4 $225.69   6.609%   $240.6059   $240.61   $240.60   $240.60  
  Purchase #5 $84.73   13.285%   $95.9864   $95.99   $96.00   $96.00  
  Purchase #6 $199.96   10.814%   $221.5837   $221.58   $221.60   $221.60  
  Purchase #7 $229.45   13.768%   $261.0407   $261.04   $261.05   $261.00  
  7 purchase totals = $1,043.57       $1,159.4602   $1,159.46   $1,159.50   $1,159.50