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	$139.46	4.546%	$145.7999	$145.80	$145.80	$145.80
Purchase #2	$58.64	9.389%	$64.1457	$64.15	$64.15	$64.10
Purchase #3	$66.51	6.865%	$71.0759	$71.08	$71.10	$71.10
Purchase #4	$211.90	4.788%	$222.0458	$222.05	$222.05	$222.00
Purchase #5	$210.61	5.469%	$222.1283	$222.13	$222.15	$222.10
Purchase #6	$54.60	10.583%	$60.3783	$60.38	$60.40	$60.40
Purchase #7	$50.71	9.691%	$55.6243	$55.62	$55.60	$55.60
7 purchase totals =	$792.43		$841.1982	$841.21	$841.25	$841.10