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	$84.69	5.423%	$89.2827	$89.28	$89.30	$89.30
Purchase #2	$120.76	3.345%	$124.7994	$124.80	$124.80	$124.80
Purchase #3	$123.97	3.369%	$128.1465	$128.15	$128.15	$128.10
Purchase #4	$67.56	7.719%	$72.775	$72.78	$72.80	$72.80
Purchase #5	$54.76	12.613%	$61.6669	$61.67	$61.65	$61.70
Purchase #6	$79.79	13.529%	$90.5848	$90.58	$90.60	$90.60
Purchase #7	$227.57	10.351%	$251.1258	$251.13	$251.15	$251.10
7 purchase totals =	$759.10		$818.3811	$818.39	$818.45	$818.40