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	$77.66	9.284%	$84.87	$84.87	$84.85	$84.90
Purchase #2	$42.34	8.388%	$45.8915	$45.89	$45.90	$45.90
Purchase #3	$229.69	7.659%	$247.282	$247.28	$247.30	$247.30
Purchase #4	$140.38	8.106%	$151.7592	$151.76	$151.75	$151.80
Purchase #5	$63.84	13.711%	$72.5931	$72.59	$72.60	$72.60
Purchase #6	$69.40	4.534%	$72.5466	$72.55	$72.55	$72.50
Purchase #7	$32.40	10.478%	$35.7949	$35.79	$35.80	$35.80
7 purchase totals =	$655.71		$710.7373	$710.73	$710.75	$710.80