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	$81.92	8.411%	$88.8103	$88.81	$88.80	$88.80
Purchase #2	$89.87	11.508%	$100.2122	$100.21	$100.20	$100.20
Purchase #3	$141.81	13.182%	$160.5034	$160.50	$160.50	$160.50
Purchase #4	$206.60	4.705%	$216.3205	$216.32	$216.30	$216.30
Purchase #5	$185.78	12.772%	$209.5078	$209.51	$209.50	$209.50
Purchase #6	$202.36	13.516%	$229.711	$229.71	$229.70	$229.70
Purchase #7	$75.75	4.123%	$78.8732	$78.87	$78.85	$78.90
7 purchase totals =	$984.09		$1,083.9384	$1,083.93	$1,083.85	$1,083.90