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	$172.79	4.166%	$179.9884	$179.99	$180.00	$180.00
Purchase #2	$85.80	4.208%	$89.4105	$89.41	$89.40	$89.40
Purchase #3	$78.91	3.397%	$81.5906	$81.59	$81.60	$81.60
Purchase #4	$108.61	7.830%	$117.1142	$117.11	$117.10	$117.10
Purchase #5	$151.73	11.717%	$169.5082	$169.51	$169.50	$169.50
Purchase #6	$154.62	12.311%	$173.6553	$173.66	$173.65	$173.70
Purchase #7	$72.33	11.807%	$80.87	$80.87	$80.85	$80.90
7 purchase totals =	$824.79		$892.1372	$892.14	$892.10	$892.20