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	$96.33	7.449%	$103.5056	$103.51	$103.50	$103.50
Purchase #2	$119.63	8.843%	$130.2089	$130.21	$130.20	$130.20
Purchase #3	$229.87	8.173%	$248.6573	$248.66	$248.65	$248.70
Purchase #4	$48.42	5.216%	$50.9456	$50.95	$50.95	$50.90
Purchase #5	$42.43	13.472%	$48.1462	$48.15	$48.15	$48.10
Purchase #6	$113.82	8.144%	$123.0895	$123.09	$123.10	$123.10
Purchase #7	$115.28	10.636%	$127.5412	$127.54	$127.55	$127.50
7 purchase totals =	$765.78		$832.0943	$832.11	$832.10	$832.00