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	$34.69	8.503%	$37.6397	$37.64	$37.65	$37.60
Purchase #2	$40.32	5.323%	$42.4662	$42.47	$42.45	$42.50
Purchase #3	$216.27	12.556%	$243.4249	$243.42	$243.40	$243.40
Purchase #4	$83.44	5.644%	$88.1494	$88.15	$88.15	$88.10
Purchase #5	$146.25	3.754%	$151.7402	$151.74	$151.75	$151.70
Purchase #6	$152.41	7.659%	$164.0831	$164.08	$164.10	$164.10
Purchase #7	$127.25	12.280%	$142.8763	$142.88	$142.90	$142.90
7 purchase totals =	$800.63		$870.3798	$870.38	$870.40	$870.30