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	$93.89	7.139%	$100.5928	$100.59	$100.60	$100.60
Purchase #2	$67.78	6.147%	$71.9464	$71.95	$71.95	$71.90
Purchase #3	$177.85	11.223%	$197.8101	$197.81	$197.80	$197.80
Purchase #4	$99.93	6.298%	$106.2236	$106.22	$106.20	$106.20
Purchase #5	$237.81	13.722%	$270.4423	$270.44	$270.45	$270.40
Purchase #6	$233.31	9.264%	$254.9238	$254.92	$254.90	$254.90
Purchase #7	$33.70	10.373%	$37.1957	$37.20	$37.20	$37.20
7 purchase totals =	$944.27		$1,039.1347	$1,039.13	$1,039.10	$1,039.00