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	$203.37	10.124%	$223.9592	$223.96	$223.95	$224.00
Purchase #2	$190.40	3.226%	$196.5423	$196.54	$196.55	$196.50
Purchase #3	$241.89	12.266%	$271.5602	$271.56	$271.55	$271.60
Purchase #4	$58.81	4.352%	$61.3694	$61.37	$61.35	$61.40
Purchase #5	$197.28	5.765%	$208.6532	$208.65	$208.65	$208.70
Purchase #6	$250.29	11.554%	$279.2085	$279.21	$279.20	$279.20
Purchase #7	$43.31	12.301%	$48.6376	$48.64	$48.65	$48.60
7 purchase totals =	$1,185.35		$1,289.9304	$1,289.93	$1,289.90	$1,290.00