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	$39.93	9.864%	$43.8687	$43.87	$43.85	$43.90
Purchase #2	$208.49	6.357%	$221.7437	$221.74	$221.75	$221.70
Purchase #3	$62.68	4.405%	$65.4411	$65.44	$65.45	$65.40
Purchase #4	$115.68	6.796%	$123.5416	$123.54	$123.55	$123.50
Purchase #5	$31.92	4.348%	$33.3079	$33.31	$33.30	$33.30
Purchase #6	$27.98	7.775%	$30.1554	$30.16	$30.15	$30.20
Purchase #7	$74.27	12.287%	$83.3956	$83.40	$83.40	$83.40
7 purchase totals =	$560.95		$601.4540	$601.46	$601.45	$601.40