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 $227.60   11.392%   $253.5282   $253.53   $253.55   $253.50  
  Purchase #2 $87.36   9.320%   $95.502   $95.50   $95.50   $95.50  
  Purchase #3 $245.99   13.509%   $279.2208   $279.22   $279.20   $279.20  
  Purchase #4 $38.71   6.157%   $41.0934   $41.09   $41.10   $41.10  
  Purchase #5 $249.61   9.282%   $272.7788   $272.78   $272.80   $272.80  
  Purchase #6 $190.55   10.556%   $210.6645   $210.66   $210.65   $210.70  
  Purchase #7 $77.94   5.566%   $82.2781   $82.28   $82.30   $82.30  
  7 purchase totals = $1,117.76       $1,235.0658   $1,235.06   $1,235.10   $1,235.10