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	$78.55	6.251%	$83.4602	$83.46	$83.45	$83.50
Purchase #2	$73.77	10.573%	$81.5697	$81.57	$81.55	$81.60
Purchase #3	$242.63	9.143%	$264.8137	$264.81	$264.80	$264.80
Purchase #4	$91.84	9.521%	$100.5841	$100.58	$100.60	$100.60
Purchase #5	$190.28	9.868%	$209.0568	$209.06	$209.05	$209.10
Purchase #6	$115.39	13.840%	$131.36	$131.36	$131.35	$131.40
Purchase #7	$162.31	3.704%	$168.322	$168.32	$168.30	$168.30
7 purchase totals =	$954.77		$1,039.1665	$1,039.16	$1,039.10	$1,039.30