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 $68.43   11.489%   $76.2919   $76.29   $76.30   $76.30  
  Purchase #2 $16.36   7.236%   $17.5438   $17.54   $17.55   $17.50  
  Purchase #3 $241.45   7.116%   $258.6316   $258.63   $258.65   $258.60  
  Purchase #4 $146.88   11.173%   $163.2909   $163.29   $163.30   $163.30  
  Purchase #5 $210.71   5.834%   $223.0028   $223.00   $223.00   $223.00  
  Purchase #6 $211.42   11.200%   $235.099   $235.10   $235.10   $235.10  
  Purchase #7 $21.98   8.558%   $23.861   $23.86   $23.85   $23.90  
  7 purchase totals = $917.23       $997.7210   $997.71   $997.75   $997.70