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 $55.86   5.563%   $58.9675   $58.97   $58.95   $59.00  
  Purchase #2 $180.45   10.108%   $198.6899   $198.69   $198.70   $198.70  
  Purchase #3 $109.28   7.219%   $117.1689   $117.17   $117.15   $117.20  
  Purchase #4 $167.59   10.167%   $184.6289   $184.63   $184.65   $184.60  
  Purchase #5 $82.42   11.602%   $91.9824   $91.98   $92.00   $92.00  
  Purchase #6 $176.50   12.331%   $198.2642   $198.26   $198.25   $198.30  
  Purchase #7 $235.93   12.521%   $265.4708   $265.47   $265.45   $265.50  
  7 purchase totals = $1,008.03       $1,115.1726   $1,115.17   $1,115.15   $1,115.30