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	$65.44	3.526%	$67.7474	$67.75	$67.75	$67.70
Purchase #2	$145.31	6.536%	$154.8075	$154.81	$154.80	$154.80
Purchase #3	$42.54	7.193%	$45.5999	$45.60	$45.60	$45.60
Purchase #4	$64.44	13.219%	$72.9583	$72.96	$72.95	$73.00
Purchase #5	$216.43	12.219%	$242.8756	$242.88	$242.90	$242.90
Purchase #6	$89.30	8.601%	$96.9807	$96.98	$97.00	$97.00
Purchase #7	$111.28	11.756%	$124.3621	$124.36	$124.35	$124.40
7 purchase totals =	$734.74		$805.3315	$805.34	$805.35	$805.40