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 $84.95   13.846%   $96.7122   $96.71   $96.70   $96.70  
  Purchase #2 $236.72   12.745%   $266.89   $266.89   $266.90   $266.90  
  Purchase #3 $224.97   12.506%   $253.1047   $253.10   $253.10   $253.10  
  Purchase #4 $200.39   12.776%   $225.9918   $225.99   $226.00   $226.00  
  Purchase #5 $27.57   11.660%   $30.7847   $30.78   $30.80   $30.80  
  Purchase #6 $91.45   5.866%   $96.8145   $96.81   $96.80   $96.80  
  Purchase #7 $128.54   11.215%   $142.9558   $142.96   $142.95   $143.00  
  7 purchase totals = $994.59       $1,113.2537   $1,113.24   $1,113.25   $1,113.30