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	$12.56	6.864%	$13.4221	$13.42	$13.40	$13.40
Purchase #2	$115.63	12.693%	$130.3069	$130.31	$130.30	$130.30
Purchase #3	$88.58	6.364%	$94.2172	$94.22	$94.20	$94.20
Purchase #4	$86.86	13.301%	$98.4132	$98.41	$98.40	$98.40
Purchase #5	$39.78	10.463%	$43.9422	$43.94	$43.95	$43.90
Purchase #6	$169.54	7.783%	$182.7353	$182.74	$182.75	$182.70
Purchase #7	$56.84	4.307%	$59.2881	$59.29	$59.30	$59.30
7 purchase totals =	$569.79		$622.3250	$622.33	$622.30	$622.20