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	$153.62	13.521%	$174.391	$174.39	$174.40	$174.40
Purchase #2	$145.50	7.728%	$156.7442	$156.74	$156.75	$156.70
Purchase #3	$218.25	5.102%	$229.3851	$229.39	$229.40	$229.40
Purchase #4	$59.28	12.749%	$66.8376	$66.84	$66.85	$66.80
Purchase #5	$145.25	7.567%	$156.2411	$156.24	$156.25	$156.20
Purchase #6	$79.44	4.322%	$82.8734	$82.87	$82.85	$82.90
Purchase #7	$23.31	6.820%	$24.8997	$24.90	$24.90	$24.90
7 purchase totals =	$824.65		$891.3721	$891.37	$891.40	$891.30