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	$91.73	11.795%	$102.5496	$102.55	$102.55	$102.50
Purchase #2	$142.80	5.235%	$150.2756	$150.28	$150.30	$150.30
Purchase #3	$189.59	11.544%	$211.4763	$211.48	$211.50	$211.50
Purchase #4	$226.67	12.171%	$254.258	$254.26	$254.25	$254.30
Purchase #5	$98.99	12.606%	$111.4687	$111.47	$111.45	$111.50
Purchase #6	$114.56	13.665%	$130.2146	$130.21	$130.20	$130.20
Purchase #7	$125.88	10.723%	$139.3781	$139.38	$139.40	$139.40
7 purchase totals =	$990.22		$1,099.6209	$1,099.63	$1,099.65	$1,099.70