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	$229.64	5.462%	$242.1829	$242.18	$242.20	$242.20
Purchase #2	$190.63	6.777%	$203.549	$203.55	$203.55	$203.50
Purchase #3	$34.85	3.144%	$35.9457	$35.95	$35.95	$35.90
Purchase #4	$178.96	9.733%	$196.3782	$196.38	$196.40	$196.40
Purchase #5	$27.75	13.188%	$31.4097	$31.41	$31.40	$31.40
Purchase #6	$9.50	10.710%	$10.5175	$10.52	$10.50	$10.50
Purchase #7	$140.73	8.449%	$152.6203	$152.62	$152.60	$152.60
7 purchase totals =	$812.06		$872.6033	$872.61	$872.60	$872.50