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 $22.68   8.616%   $24.6341   $24.63   $24.65   $24.60  
  Purchase #2 $226.78   5.239%   $238.661   $238.66   $238.65   $238.70  
  Purchase #3 $20.56   5.267%   $21.6429   $21.64   $21.65   $21.60  
  Purchase #4 $203.88   8.390%   $220.9855   $220.99   $221.00   $221.00  
  Purchase #5 $238.69   11.402%   $265.9054   $265.91   $265.90   $265.90  
  Purchase #6 $75.33   9.461%   $82.457   $82.46   $82.45   $82.50  
  Purchase #7 $24.52   4.623%   $25.6536   $25.65   $25.65   $25.70  
  7 purchase totals = $812.44       $879.9395   $879.94   $879.95   $880.00