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	$25.41	4.191%	$26.4749	$26.47	$26.45	$26.50
Purchase #2	$83.56	13.178%	$94.5715	$94.57	$94.55	$94.60
Purchase #3	$180.85	4.417%	$188.8381	$188.84	$188.85	$188.80
Purchase #4	$163.95	6.357%	$174.3723	$174.37	$174.35	$174.40
Purchase #5	$40.36	8.509%	$43.7942	$43.79	$43.80	$43.80
Purchase #6	$39.25	3.323%	$40.5543	$40.55	$40.55	$40.60
Purchase #7	$93.44	7.752%	$100.6835	$100.68	$100.70	$100.70
7 purchase totals =	$626.82		$669.2888	$669.27	$669.25	$669.40