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	$51.59	5.517%	$54.4362	$54.44	$54.45	$54.40
Purchase #2	$22.66	5.661%	$23.9428	$23.94	$23.95	$23.90
Purchase #3	$37.66	6.865%	$40.2454	$40.25	$40.25	$40.20
Purchase #4	$212.50	4.573%	$222.2176	$222.22	$222.20	$222.20
Purchase #5	$88.41	3.542%	$91.5415	$91.54	$91.55	$91.50
Purchase #6	$193.61	12.310%	$217.4434	$217.44	$217.45	$217.40
Purchase #7	$183.56	4.228%	$191.3209	$191.32	$191.30	$191.30
7 purchase totals =	$789.99		$841.1478	$841.15	$841.15	$840.90