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	$91.44	5.139%	$96.1391	$96.14	$96.15	$96.10
Purchase #2	$53.39	12.112%	$59.8566	$59.86	$59.85	$59.90
Purchase #3	$143.28	13.733%	$162.9566	$162.96	$162.95	$163.00
Purchase #4	$205.93	11.344%	$229.2907	$229.29	$229.30	$229.30
Purchase #5	$191.49	6.457%	$203.8545	$203.85	$203.85	$203.90
Purchase #6	$79.37	11.549%	$88.5364	$88.54	$88.55	$88.50
Purchase #7	$95.45	4.755%	$99.9886	$99.99	$100.00	$100.00
7 purchase totals =	$860.35		$940.6225	$940.63	$940.65	$940.70