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	$36.75	5.450%	$38.7529	$38.75	$38.75	$38.80
Purchase #2	$198.46	12.746%	$223.7557	$223.76	$223.75	$223.80
Purchase #3	$202.71	9.798%	$222.5715	$222.57	$222.55	$222.60
Purchase #4	$77.65	11.650%	$86.6962	$86.70	$86.70	$86.70
Purchase #5	$249.62	3.417%	$258.1495	$258.15	$258.15	$258.10
Purchase #6	$63.49	13.819%	$72.2637	$72.26	$72.25	$72.30
Purchase #7	$212.87	4.518%	$222.4875	$222.49	$222.50	$222.50
7 purchase totals =	$1,041.55		$1,124.6770	$1,124.68	$1,124.65	$1,124.80