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 $61.63   6.261%   $65.4887   $65.49   $65.50   $65.50  
  Purchase #2 $191.77   13.870%   $218.3685   $218.37   $218.35   $218.40  
  Purchase #3 $110.37   7.241%   $118.3619   $118.36   $118.35   $118.40  
  Purchase #4 $45.45   9.137%   $49.6028   $49.60   $49.60   $49.60  
  Purchase #5 $33.93   3.862%   $35.2404   $35.24   $35.25   $35.20  
  Purchase #6 $240.85   8.373%   $261.0164   $261.02   $261.00   $261.00  
  Purchase #7 $214.95   5.238%   $226.2091   $226.21   $226.20   $226.20  
  7 purchase totals = $898.95       $974.2878   $974.29   $974.25   $974.30