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 $181.79   4.802%   $190.5196   $190.52   $190.50   $190.50  
  Purchase #2 $32.31   8.522%   $35.0635   $35.06   $35.05   $35.10  
  Purchase #3 $246.63   4.797%   $258.4608   $258.46   $258.45   $258.50  
  Purchase #4 $111.45   11.404%   $124.1598   $124.16   $124.15   $124.20  
  Purchase #5 $158.77   11.495%   $177.0206   $177.02   $177.00   $177.00  
  Purchase #6 $79.99   11.225%   $88.9689   $88.97   $88.95   $89.00  
  Purchase #7 $49.49   5.498%   $52.211   $52.21   $52.20   $52.20  
  7 purchase totals = $860.43       $926.4042   $926.40   $926.30   $926.50