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 $248.58   6.733%   $265.3169   $265.32   $265.30   $265.30  
  Purchase #2 $173.67   5.325%   $182.9179   $182.92   $182.90   $182.90  
  Purchase #3 $13.45   9.427%   $14.7179   $14.72   $14.70   $14.70  
  Purchase #4 $11.80   6.656%   $12.5854   $12.59   $12.60   $12.60  
  Purchase #5 $72.57   5.490%   $76.5541   $76.55   $76.55   $76.60  
  Purchase #6 $211.44   6.671%   $225.5452   $225.55   $225.55   $225.50  
  Purchase #7 $22.49   10.138%   $24.77   $24.77   $24.75   $24.80  
  7 purchase totals = $754.00       $802.4074   $802.42   $802.35   $802.40