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	$233.52	8.753%	$253.96	$253.96	$253.95	$254.00
Purchase #2	$81.86	10.581%	$90.5216	$90.52	$90.50	$90.50
Purchase #3	$150.62	11.470%	$167.8961	$167.90	$167.90	$167.90
Purchase #4	$45.53	11.297%	$50.6735	$50.67	$50.65	$50.70
Purchase #5	$38.85	13.698%	$44.1717	$44.17	$44.15	$44.20
Purchase #6	$189.90	11.836%	$212.3766	$212.38	$212.40	$212.40
Purchase #7	$31.66	12.205%	$35.5241	$35.52	$35.50	$35.50
7 purchase totals =	$771.94		$855.1236	$855.12	$855.05	$855.20