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 $56.61   9.512%   $61.9947   $61.99   $62.00   $62.00  
  Purchase #2 $82.71   6.764%   $88.3045   $88.30   $88.30   $88.30  
  Purchase #3 $135.41   3.403%   $140.018   $140.02   $140.00   $140.00  
  Purchase #4 $78.71   8.329%   $85.2658   $85.27   $85.25   $85.30  
  Purchase #5 $124.77   4.843%   $130.8126   $130.81   $130.80   $130.80  
  Purchase #6 $173.69   7.420%   $186.5778   $186.58   $186.60   $186.60  
  Purchase #7 $199.72   4.270%   $208.248   $208.25   $208.25   $208.20  
  7 purchase totals = $851.62       $901.2214   $901.22   $901.20   $901.20