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	$123.80	3.331%	$127.9238	$127.92	$127.90	$127.90
Purchase #2	$179.85	6.315%	$191.2075	$191.21	$191.20	$191.20
Purchase #3	$48.95	6.272%	$52.0201	$52.02	$52.00	$52.00
Purchase #4	$94.95	10.173%	$104.6093	$104.61	$104.60	$104.60
Purchase #5	$228.56	8.431%	$247.8299	$247.83	$247.85	$247.80
Purchase #6	$89.69	8.310%	$97.1432	$97.14	$97.15	$97.10
Purchase #7	$172.95	3.377%	$178.7905	$178.79	$178.80	$178.80
7 purchase totals =	$938.75		$999.5243	$999.52	$999.50	$999.40