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	$151.33	12.190%	$169.7771	$169.78	$169.80	$169.80
Purchase #2	$164.34	4.239%	$171.3064	$171.31	$171.30	$171.30
Purchase #3	$59.32	6.191%	$62.9925	$62.99	$63.00	$63.00
Purchase #4	$57.40	9.428%	$62.8117	$62.81	$62.80	$62.80
Purchase #5	$146.68	3.191%	$151.3606	$151.36	$151.35	$151.40
Purchase #6	$123.46	8.432%	$133.8701	$133.87	$133.85	$133.90
Purchase #7	$72.92	12.848%	$82.2888	$82.29	$82.30	$82.30
7 purchase totals =	$775.45		$834.4072	$834.41	$834.40	$834.50