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	$115.34	13.707%	$131.1497	$131.15	$131.15	$131.10
Purchase #2	$6.31	6.319%	$6.7087	$6.71	$6.70	$6.70
Purchase #3	$227.61	5.476%	$240.0739	$240.07	$240.05	$240.10
Purchase #4	$181.95	5.362%	$191.7062	$191.71	$191.70	$191.70
Purchase #5	$77.30	3.728%	$80.1817	$80.18	$80.20	$80.20
Purchase #6	$45.79	5.805%	$48.4481	$48.45	$48.45	$48.40
Purchase #7	$29.52	12.780%	$33.2927	$33.29	$33.30	$33.30
7 purchase totals =	$683.82		$731.5610	$731.56	$731.55	$731.50