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 $228.25   4.272%   $238.0008   $238.00   $238.00   $238.00  
  Purchase #2 $31.91   11.681%   $35.6374   $35.64   $35.65   $35.60  
  Purchase #3 $107.71   12.298%   $120.9562   $120.96   $120.95   $121.00  
  Purchase #4 $112.63   9.143%   $122.9278   $122.93   $122.95   $122.90  
  Purchase #5 $153.55   3.321%   $158.6494   $158.65   $158.65   $158.60  
  Purchase #6 $93.55   10.726%   $103.5842   $103.58   $103.60   $103.60  
  Purchase #7 $224.85   4.275%   $234.4623   $234.46   $234.45   $234.50  
  7 purchase totals = $952.45       $1,014.2181   $1,014.22   $1,014.25   $1,014.20