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	$108.59	6.551%	$115.7037	$115.70	$115.70	$115.70
Purchase #2	$82.34	3.625%	$85.3248	$85.32	$85.30	$85.30
Purchase #3	$159.54	11.813%	$178.3865	$178.39	$178.40	$178.40
Purchase #4	$56.78	6.744%	$60.6092	$60.61	$60.60	$60.60
Purchase #5	$91.62	5.198%	$96.3824	$96.38	$96.40	$96.40
Purchase #6	$162.59	10.152%	$179.0961	$179.10	$179.10	$179.10
Purchase #7	$240.83	6.264%	$255.9156	$255.92	$255.90	$255.90
7 purchase totals =	$902.29		$971.4183	$971.42	$971.40	$971.40