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 $42.91   3.809%   $44.5444   $44.54   $44.55   $44.50  
  Purchase #2 $13.61   4.158%   $14.1759   $14.18   $14.20   $14.20  
  Purchase #3 $56.61   10.388%   $62.4906   $62.49   $62.50   $62.50  
  Purchase #4 $235.57   11.178%   $261.902   $261.90   $261.90   $261.90  
  Purchase #5 $218.94   4.722%   $229.2783   $229.28   $229.30   $229.30  
  Purchase #6 $62.28   3.837%   $64.6697   $64.67   $64.65   $64.70  
  Purchase #7 $127.46   3.331%   $131.7057   $131.71   $131.70   $131.70  
  7 purchase totals = $757.38       $808.7666   $808.77   $808.80   $808.80