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	$100.88	8.359%	$109.3126	$109.31	$109.30	$109.30
Purchase #2	$74.55	3.654%	$77.2741	$77.27	$77.25	$77.30
Purchase #3	$143.77	8.758%	$156.3614	$156.36	$156.35	$156.40
Purchase #4	$54.37	4.340%	$56.7297	$56.73	$56.75	$56.70
Purchase #5	$145.46	3.504%	$150.5569	$150.56	$150.55	$150.60
Purchase #6	$144.82	9.177%	$158.1101	$158.11	$158.10	$158.10
Purchase #7	$124.25	3.772%	$128.9367	$128.94	$128.95	$128.90
7 purchase totals =	$788.10		$837.2815	$837.28	$837.25	$837.30