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	$82.77	9.785%	$90.869	$90.87	$90.85	$90.90
Purchase #2	$203.48	9.657%	$223.1301	$223.13	$223.15	$223.10
Purchase #3	$67.87	10.170%	$74.7724	$74.77	$74.75	$74.80
Purchase #4	$83.85	5.332%	$88.3209	$88.32	$88.30	$88.30
Purchase #5	$51.98	11.773%	$58.0996	$58.10	$58.10	$58.10
Purchase #6	$245.46	7.710%	$264.385	$264.39	$264.40	$264.40
Purchase #7	$48.84	6.315%	$51.9242	$51.92	$51.90	$51.90
7 purchase totals =	$784.25		$851.5012	$851.50	$851.45	$851.50