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	$79.70	12.611%	$89.751	$89.75	$89.75	$89.80
Purchase #2	$34.33	3.147%	$35.4104	$35.41	$35.40	$35.40
Purchase #3	$129.74	3.701%	$134.5417	$134.54	$134.55	$134.50
Purchase #4	$65.92	11.444%	$73.4639	$73.46	$73.45	$73.50
Purchase #5	$249.77	5.747%	$264.1243	$264.12	$264.10	$264.10
Purchase #6	$178.94	7.481%	$192.3265	$192.33	$192.35	$192.30
Purchase #7	$10.46	12.164%	$11.7324	$11.73	$11.75	$11.70
7 purchase totals =	$748.86		$801.3502	$801.34	$801.35	$801.30