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	$147.45	4.601%	$154.2342	$154.23	$154.25	$154.20
Purchase #2	$249.82	11.536%	$278.6392	$278.64	$278.65	$278.60
Purchase #3	$115.29	7.420%	$123.8445	$123.84	$123.85	$123.80
Purchase #4	$7.86	9.597%	$8.6143	$8.61	$8.60	$8.60
Purchase #5	$140.98	9.781%	$154.7693	$154.77	$154.75	$154.80
Purchase #6	$50.83	4.751%	$53.2449	$53.24	$53.25	$53.20
Purchase #7	$10.59	5.280%	$11.1492	$11.15	$11.15	$11.10
7 purchase totals =	$722.82		$784.4956	$784.48	$784.50	$784.30