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 $61.59   7.762%   $66.3706   $66.37   $66.35   $66.40  
  Purchase #2 $70.79   8.165%   $76.57   $76.57   $76.55   $76.60  
  Purchase #3 $178.78   5.608%   $188.806   $188.81   $188.80   $188.80  
  Purchase #4 $126.76   10.402%   $139.9456   $139.95   $139.95   $139.90  
  Purchase #5 $137.25   6.133%   $145.6675   $145.67   $145.65   $145.70  
  Purchase #6 $230.57   5.178%   $242.5089   $242.51   $242.50   $242.50  
  Purchase #7 $214.49   3.603%   $222.2181   $222.22   $222.20   $222.20  
  7 purchase totals = $1,020.23       $1,082.0867   $1,082.10   $1,082.00   $1,082.10