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	$98.67	13.333%	$111.8257	$111.83	$111.85	$111.80
Purchase #2	$72.75	6.336%	$77.3594	$77.36	$77.35	$77.40
Purchase #3	$35.62	9.454%	$38.9875	$38.99	$39.00	$39.00
Purchase #4	$64.40	13.103%	$72.8383	$72.84	$72.85	$72.80
Purchase #5	$183.54	6.831%	$196.0776	$196.08	$196.10	$196.10
Purchase #6	$110.31	12.482%	$124.0789	$124.08	$124.10	$124.10
Purchase #7	$140.30	10.346%	$154.8154	$154.82	$154.80	$154.80
7 purchase totals =	$705.59		$775.9828	$776.00	$776.05	$776.00