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	$149.72	3.533%	$155.0096	$155.01	$155.00	$155.00
Purchase #2	$199.65	11.208%	$222.0268	$222.03	$222.05	$222.00
Purchase #3	$204.72	3.140%	$211.1482	$211.15	$211.15	$211.10
Purchase #4	$189.37	10.746%	$209.7197	$209.72	$209.70	$209.70
Purchase #5	$247.96	4.274%	$258.5578	$258.56	$258.55	$258.60
Purchase #6	$235.48	12.458%	$264.8161	$264.82	$264.80	$264.80
Purchase #7	$196.58	11.757%	$219.6919	$219.69	$219.70	$219.70
7 purchase totals =	$1,423.48		$1,540.9701	$1,540.98	$1,540.95	$1,540.90