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 $213.26   5.170%   $224.2855   $224.29   $224.30   $224.30  
  Purchase #2 $38.35   9.196%   $41.8767   $41.88   $41.90   $41.90  
  Purchase #3 $11.83   3.641%   $12.2607   $12.26   $12.25   $12.30  
  Purchase #4 $114.26   5.657%   $120.7237   $120.72   $120.70   $120.70  
  Purchase #5 $52.73   6.621%   $56.2213   $56.22   $56.20   $56.20  
  Purchase #6 $55.69   5.403%   $58.6989   $58.70   $58.70   $58.70  
  Purchase #7 $234.86   3.165%   $242.2933   $242.29   $242.30   $242.30  
  7 purchase totals = $720.98       $756.3601   $756.36   $756.35   $756.40