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	$33.98	9.290%	$37.1367	$37.14	$37.15	$37.10
Purchase #2	$28.75	4.492%	$30.0415	$30.04	$30.05	$30.00
Purchase #3	$42.68	5.489%	$45.0227	$45.02	$45.00	$45.00
Purchase #4	$103.29	11.839%	$115.5185	$115.52	$115.50	$115.50
Purchase #5	$170.32	7.130%	$182.4638	$182.46	$182.45	$182.50
Purchase #6	$123.39	9.349%	$134.9257	$134.93	$134.95	$134.90
Purchase #7	$160.64	7.353%	$172.4519	$172.45	$172.45	$172.50
7 purchase totals =	$663.05		$717.5608	$717.56	$717.55	$717.50