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	$78.37	6.343%	$83.341	$83.34	$83.35	$83.30
Purchase #2	$146.33	13.627%	$166.2704	$166.27	$166.25	$166.30
Purchase #3	$223.39	8.162%	$241.6231	$241.62	$241.60	$241.60
Purchase #4	$104.98	9.190%	$114.6277	$114.63	$114.65	$114.60
Purchase #5	$219.36	8.343%	$237.6612	$237.66	$237.65	$237.70
Purchase #6	$108.75	4.384%	$113.5176	$113.52	$113.50	$113.50
Purchase #7	$234.77	3.654%	$243.3485	$243.35	$243.35	$243.30
7 purchase totals =	$1,115.95		$1,200.3895	$1,200.39	$1,200.35	$1,200.30