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	$147.62	4.655%	$154.4917	$154.49	$154.50	$154.50
Purchase #2	$75.46	6.231%	$80.1619	$80.16	$80.15	$80.20
Purchase #3	$67.47	3.533%	$69.8537	$69.85	$69.85	$69.90
Purchase #4	$144.73	9.183%	$158.0206	$158.02	$158.00	$158.00
Purchase #5	$52.65	13.860%	$59.9473	$59.95	$59.95	$59.90
Purchase #6	$114.91	11.700%	$128.3545	$128.35	$128.35	$128.40
Purchase #7	$25.35	10.315%	$27.9649	$27.96	$27.95	$28.00
7 purchase totals =	$628.19		$678.7946	$678.78	$678.75	$678.90