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	$50.45	4.772%	$52.8575	$52.86	$52.85	$52.90
Purchase #2	$42.26	10.608%	$46.7429	$46.74	$46.75	$46.70
Purchase #3	$142.66	13.654%	$162.1388	$162.14	$162.15	$162.10
Purchase #4	$104.63	7.575%	$112.5557	$112.56	$112.55	$112.60
Purchase #5	$112.28	9.421%	$122.8579	$122.86	$122.85	$122.90
Purchase #6	$62.92	7.483%	$67.6283	$67.63	$67.65	$67.60
Purchase #7	$26.52	6.224%	$28.1706	$28.17	$28.15	$28.20
7 purchase totals =	$541.72		$592.9517	$592.96	$592.95	$593.00