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	$37.88	8.588%	$41.1331	$41.13	$41.15	$41.10
Purchase #2	$77.56	7.732%	$83.5569	$83.56	$83.55	$83.60
Purchase #3	$228.38	13.838%	$259.9832	$259.98	$260.00	$260.00
Purchase #4	$89.88	10.210%	$99.0567	$99.06	$99.05	$99.10
Purchase #5	$77.26	3.496%	$79.961	$79.96	$79.95	$80.00
Purchase #6	$54.67	13.818%	$62.2243	$62.22	$62.20	$62.20
Purchase #7	$217.75	11.303%	$242.3623	$242.36	$242.35	$242.40
7 purchase totals =	$783.38		$868.2775	$868.27	$868.25	$868.40