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 $61.72   10.178%   $68.0019   $68.00   $68.00   $68.00  
  Purchase #2 $201.64   10.271%   $222.3504   $222.35   $222.35   $222.40  
  Purchase #3 $134.36   6.106%   $142.564   $142.56   $142.55   $142.60  
  Purchase #4 $228.50   3.569%   $236.6552   $236.66   $236.65   $236.70  
  Purchase #5 $41.57   13.738%   $47.2809   $47.28   $47.30   $47.30  
  Purchase #6 $250.42   4.215%   $260.9752   $260.98   $261.00   $261.00  
  Purchase #7 $227.49   11.201%   $252.9712   $252.97   $252.95   $253.00  
  7 purchase totals = $1,145.70       $1,230.7988   $1,230.80   $1,230.80   $1,231.00