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	$72.68	13.614%	$82.5747	$82.57	$82.55	$82.60
Purchase #2	$143.54	9.259%	$156.8304	$156.83	$156.85	$156.80
Purchase #3	$37.99	7.682%	$40.9084	$40.91	$40.90	$40.90
Purchase #4	$101.62	7.296%	$109.0342	$109.03	$109.05	$109.00
Purchase #5	$14.76	11.584%	$16.4698	$16.47	$16.45	$16.50
Purchase #6	$97.58	7.117%	$104.5248	$104.52	$104.50	$104.50
Purchase #7	$136.69	9.229%	$149.3051	$149.31	$149.30	$149.30
7 purchase totals =	$604.86		$659.6474	$659.64	$659.60	$659.60