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	$141.87	4.489%	$148.2385	$148.24	$148.25	$148.20
Purchase #2	$135.43	3.804%	$140.5818	$140.58	$140.60	$140.60
Purchase #3	$171.55	11.207%	$190.7756	$190.78	$190.80	$190.80
Purchase #4	$231.49	10.646%	$256.1344	$256.13	$256.15	$256.10
Purchase #5	$38.87	12.399%	$43.6895	$43.69	$43.70	$43.70
Purchase #6	$238.45	9.377%	$260.8095	$260.81	$260.80	$260.80
Purchase #7	$181.74	10.213%	$200.3011	$200.30	$200.30	$200.30
7 purchase totals =	$1,139.40		$1,240.5304	$1,240.53	$1,240.60	$1,240.50