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	$38.65	6.407%	$41.1263	$41.13	$41.15	$41.10
Purchase #2	$128.57	8.272%	$139.2053	$139.21	$139.20	$139.20
Purchase #3	$148.61	4.290%	$154.9854	$154.99	$155.00	$155.00
Purchase #4	$56.69	13.668%	$64.4384	$64.44	$64.45	$64.40
Purchase #5	$101.69	9.725%	$111.5794	$111.58	$111.60	$111.60
Purchase #6	$248.41	8.419%	$269.3236	$269.32	$269.30	$269.30
Purchase #7	$10.91	8.874%	$11.8782	$11.88	$11.90	$11.90
7 purchase totals =	$733.53		$792.5366	$792.55	$792.60	$792.50