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 $244.46   8.641%   $265.5838   $265.58   $265.60   $265.60  
  Purchase #2 $103.54   12.867%   $116.8625   $116.86   $116.85   $116.90  
  Purchase #3 $180.95   6.635%   $192.956   $192.96   $192.95   $193.00  
  Purchase #4 $213.86   3.716%   $221.807   $221.81   $221.80   $221.80  
  Purchase #5 $196.37   8.134%   $212.3427   $212.34   $212.35   $212.30  
  Purchase #6 $32.46   6.179%   $34.4657   $34.47   $34.45   $34.50  
  Purchase #7 $32.31   5.196%   $33.9888   $33.99   $34.00   $34.00  
  7 purchase totals = $1,003.95       $1,078.0065   $1,078.01   $1,078.00   $1,078.10