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	$72.82	13.738%	$82.824	$82.82	$82.80	$82.80
Purchase #2	$191.63	4.650%	$200.5408	$200.54	$200.55	$200.50
Purchase #3	$46.77	12.819%	$52.7654	$52.77	$52.75	$52.80
Purchase #4	$133.84	6.466%	$142.4941	$142.49	$142.50	$142.50
Purchase #5	$122.75	4.640%	$128.4456	$128.45	$128.45	$128.40
Purchase #6	$37.75	9.464%	$41.3227	$41.32	$41.30	$41.30
Purchase #7	$222.67	12.424%	$250.3345	$250.33	$250.35	$250.30
7 purchase totals =	$828.23		$898.7271	$898.72	$898.70	$898.60