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	$55.88	10.113%	$61.5311	$61.53	$61.55	$61.50
Purchase #2	$245.64	10.277%	$270.8844	$270.88	$270.90	$270.90
Purchase #3	$237.49	8.473%	$257.6125	$257.61	$257.60	$257.60
Purchase #4	$79.55	13.483%	$90.2757	$90.28	$90.30	$90.30
Purchase #5	$175.90	3.116%	$181.381	$181.38	$181.40	$181.40
Purchase #6	$82.66	12.288%	$92.8173	$92.82	$92.80	$92.80
Purchase #7	$42.70	12.553%	$48.0601	$48.06	$48.05	$48.10
7 purchase totals =	$919.82		$1,002.5621	$1,002.56	$1,002.60	$1,002.60