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	$80.92	10.685%	$89.5663	$89.57	$89.55	$89.60
Purchase #2	$73.75	9.612%	$80.8389	$80.84	$80.85	$80.80
Purchase #3	$51.87	6.222%	$55.0974	$55.10	$55.10	$55.10
Purchase #4	$49.81	6.567%	$53.081	$53.08	$53.10	$53.10
Purchase #5	$54.64	9.265%	$59.7024	$59.70	$59.70	$59.70
Purchase #6	$208.55	6.242%	$221.5677	$221.57	$221.55	$221.60
Purchase #7	$115.87	12.449%	$130.2947	$130.29	$130.30	$130.30
7 purchase totals =	$635.41		$690.1484	$690.15	$690.15	$690.20