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	$161.41	12.837%	$182.1302	$182.13	$182.15	$182.10
Purchase #2	$131.74	11.171%	$146.4567	$146.46	$146.45	$146.50
Purchase #3	$248.52	8.605%	$269.9051	$269.91	$269.90	$269.90
Purchase #4	$19.86	13.422%	$22.5256	$22.53	$22.55	$22.50
Purchase #5	$180.80	10.318%	$199.4549	$199.45	$199.45	$199.50
Purchase #6	$36.94	13.377%	$41.8815	$41.88	$41.90	$41.90
Purchase #7	$42.40	9.579%	$46.4615	$46.46	$46.45	$46.50
7 purchase totals =	$821.67		$908.8155	$908.82	$908.85	$908.90