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	$67.72	9.649%	$74.2543	$74.25	$74.25	$74.30
Purchase #2	$234.54	8.298%	$254.0021	$254.00	$254.00	$254.00
Purchase #3	$103.88	11.305%	$115.6236	$115.62	$115.60	$115.60
Purchase #4	$90.48	10.774%	$100.2283	$100.23	$100.25	$100.20
Purchase #5	$11.41	3.601%	$11.8209	$11.82	$11.80	$11.80
Purchase #6	$67.84	7.371%	$72.8405	$72.84	$72.85	$72.80
Purchase #7	$145.65	10.244%	$160.5704	$160.57	$160.55	$160.60
7 purchase totals =	$721.52		$789.3401	$789.33	$789.30	$789.30