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	$83.66	8.773%	$90.9995	$91.00	$91.00	$91.00
Purchase #2	$59.78	9.788%	$65.6313	$65.63	$65.65	$65.60
Purchase #3	$109.92	4.784%	$115.1786	$115.18	$115.20	$115.20
Purchase #4	$36.87	10.484%	$40.7355	$40.74	$40.75	$40.70
Purchase #5	$77.61	6.828%	$82.9092	$82.91	$82.90	$82.90
Purchase #6	$53.30	12.481%	$59.9524	$59.95	$59.95	$60.00
Purchase #7	$97.45	7.134%	$104.4021	$104.40	$104.40	$104.40
7 purchase totals =	$518.59		$559.8086	$559.81	$559.85	$559.80