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	$38.59	4.716%	$40.4099	$40.41	$40.40	$40.40
Purchase #2	$58.26	7.343%	$62.538	$62.54	$62.55	$62.50
Purchase #3	$147.60	3.135%	$152.2273	$152.23	$152.25	$152.20
Purchase #4	$101.98	12.276%	$114.4991	$114.50	$114.50	$114.50
Purchase #5	$74.97	7.217%	$80.3806	$80.38	$80.40	$80.40
Purchase #6	$85.92	3.691%	$89.0913	$89.09	$89.10	$89.10
Purchase #7	$250.64	12.640%	$282.3209	$282.32	$282.30	$282.30
7 purchase totals =	$757.96		$821.4671	$821.47	$821.50	$821.40