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	$108.67	3.152%	$112.0953	$112.10	$112.10	$112.10
Purchase #2	$35.42	8.687%	$38.4969	$38.50	$38.50	$38.50
Purchase #3	$163.78	5.317%	$172.4882	$172.49	$172.50	$172.50
Purchase #4	$169.36	13.751%	$192.6487	$192.65	$192.65	$192.60
Purchase #5	$78.90	9.700%	$86.5533	$86.55	$86.55	$86.60
Purchase #6	$102.40	3.407%	$105.8888	$105.89	$105.90	$105.90
Purchase #7	$195.25	4.858%	$204.7352	$204.74	$204.75	$204.70
7 purchase totals =	$853.78		$912.9064	$912.92	$912.95	$912.90