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	$92.78	8.398%	$100.5717	$100.57	$100.55	$100.60
Purchase #2	$248.84	9.640%	$272.8282	$272.83	$272.85	$272.80
Purchase #3	$94.25	4.381%	$98.3791	$98.38	$98.40	$98.40
Purchase #4	$142.25	10.680%	$157.4423	$157.44	$157.45	$157.40
Purchase #5	$30.75	10.127%	$33.8641	$33.86	$33.85	$33.90
Purchase #6	$104.69	6.258%	$111.2415	$111.24	$111.25	$111.20
Purchase #7	$15.28	13.560%	$17.352	$17.35	$17.35	$17.40
7 purchase totals =	$728.84		$791.6789	$791.67	$791.70	$791.70