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	$49.59	11.218%	$55.153	$55.15	$55.15	$55.20
Purchase #2	$170.80	7.577%	$183.7415	$183.74	$183.75	$183.70
Purchase #3	$141.27	11.244%	$157.1544	$157.15	$157.15	$157.20
Purchase #4	$33.70	9.849%	$37.0191	$37.02	$37.00	$37.00
Purchase #5	$111.88	10.728%	$123.8825	$123.88	$123.90	$123.90
Purchase #6	$27.91	3.443%	$28.8709	$28.87	$28.85	$28.90
Purchase #7	$169.79	11.164%	$188.7454	$188.75	$188.75	$188.70
7 purchase totals =	$704.94		$774.5668	$774.56	$774.55	$774.60