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	$71.33	4.279%	$74.3822	$74.38	$74.40	$74.40
Purchase #2	$155.70	10.208%	$171.5939	$171.59	$171.60	$171.60
Purchase #3	$205.64	13.683%	$233.7777	$233.78	$233.80	$233.80
Purchase #4	$185.96	5.649%	$196.4649	$196.46	$196.45	$196.50
Purchase #5	$51.65	6.760%	$55.1415	$55.14	$55.15	$55.10
Purchase #6	$136.37	8.138%	$147.4678	$147.47	$147.45	$147.50
Purchase #7	$90.51	5.340%	$95.3432	$95.34	$95.35	$95.30
7 purchase totals =	$897.16		$974.1712	$974.16	$974.20	$974.20