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 $208.63   10.375%   $230.2754   $230.28   $230.30   $230.30  
  Purchase #2 $88.94   8.322%   $96.3416   $96.34   $96.35   $96.30  
  Purchase #3 $176.64   6.461%   $188.0527   $188.05   $188.05   $188.10  
  Purchase #4 $24.86   4.529%   $25.9859   $25.99   $26.00   $26.00  
  Purchase #5 $58.94   4.174%   $61.4002   $61.40   $61.40   $61.40  
  Purchase #6 $190.49   3.104%   $196.4028   $196.40   $196.40   $196.40  
  Purchase #7 $243.66   8.825%   $265.163   $265.16   $265.15   $265.20  
  7 purchase totals = $992.16       $1,063.6216   $1,063.62   $1,063.65   $1,063.70