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	$19.26	11.781%	$21.529	$21.53	$21.55	$21.50
Purchase #2	$39.29	3.688%	$40.739	$40.74	$40.75	$40.70
Purchase #3	$112.30	10.247%	$123.8074	$123.81	$123.80	$123.80
Purchase #4	$233.30	8.772%	$253.7651	$253.77	$253.75	$253.80
Purchase #5	$75.46	4.311%	$78.7131	$78.71	$78.70	$78.70
Purchase #6	$154.58	10.842%	$171.3396	$171.34	$171.35	$171.30
Purchase #7	$235.76	13.305%	$267.1279	$267.13	$267.15	$267.10
7 purchase totals =	$869.95		$957.0211	$957.03	$957.05	$956.90