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	$42.91	6.727%	$45.7966	$45.80	$45.80	$45.80
Purchase #2	$53.53	12.229%	$60.0762	$60.08	$60.10	$60.10
Purchase #3	$111.56	6.695%	$119.0289	$119.03	$119.05	$119.00
Purchase #4	$71.32	9.739%	$78.2659	$78.27	$78.25	$78.30
Purchase #5	$73.75	8.867%	$80.2894	$80.29	$80.30	$80.30
Purchase #6	$80.73	11.244%	$89.8073	$89.81	$89.80	$89.80
Purchase #7	$92.71	12.451%	$104.2533	$104.25	$104.25	$104.30
7 purchase totals =	$526.51		$577.5176	$577.53	$577.55	$577.60