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 $46.79   13.739%   $53.2185   $53.22   $53.20   $53.20  
  Purchase #2 $59.41   13.783%   $67.5985   $67.60   $67.60   $67.60  
  Purchase #3 $61.33   13.535%   $69.631   $69.63   $69.65   $69.60  
  Purchase #4 $218.49   7.536%   $234.9554   $234.96   $234.95   $235.00  
  Purchase #5 $228.65   10.750%   $253.2299   $253.23   $253.25   $253.20  
  Purchase #6 $97.93   4.376%   $102.2154   $102.22   $102.20   $102.20  
  Purchase #7 $221.99   13.476%   $251.9054   $251.91   $251.90   $251.90  
  7 purchase totals = $934.59       $1,032.7541   $1,032.77   $1,032.75   $1,032.70