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	$133.69	4.713%	$139.9908	$139.99	$140.00	$140.00
Purchase #2	$147.70	5.139%	$155.2903	$155.29	$155.30	$155.30
Purchase #3	$133.54	6.576%	$142.3216	$142.32	$142.30	$142.30
Purchase #4	$51.43	12.340%	$57.7765	$57.78	$57.80	$57.80
Purchase #5	$141.40	6.332%	$150.3534	$150.35	$150.35	$150.40
Purchase #6	$71.36	3.129%	$73.5929	$73.59	$73.60	$73.60
Purchase #7	$53.42	13.838%	$60.8123	$60.81	$60.80	$60.80
7 purchase totals =	$732.54		$780.1378	$780.13	$780.15	$780.20