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 $161.98   13.603%   $184.0141   $184.01   $184.00   $184.00  
  Purchase #2 $35.67   5.534%   $37.644   $37.64   $37.65   $37.60  
  Purchase #3 $207.82   8.872%   $226.2578   $226.26   $226.25   $226.30  
  Purchase #4 $250.76   8.319%   $271.6207   $271.62   $271.60   $271.60  
  Purchase #5 $166.66   10.498%   $184.156   $184.16   $184.15   $184.20  
  Purchase #6 $218.90   7.277%   $234.8294   $234.83   $234.85   $234.80  
  Purchase #7 $76.62   6.307%   $81.4524   $81.45   $81.45   $81.50  
  7 purchase totals = $1,118.41       $1,219.9744   $1,219.97   $1,219.95   $1,220.00