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	$226.62	10.677%	$250.8162	$250.82	$250.80	$250.80
Purchase #2	$106.93	4.222%	$111.4446	$111.44	$111.45	$111.40
Purchase #3	$20.45	4.546%	$21.3797	$21.38	$21.40	$21.40
Purchase #4	$42.73	6.689%	$45.5882	$45.59	$45.60	$45.60
Purchase #5	$204.27	9.305%	$223.2773	$223.28	$223.30	$223.30
Purchase #6	$189.97	4.663%	$198.8283	$198.83	$198.85	$198.80
Purchase #7	$248.51	13.603%	$282.3148	$282.31	$282.30	$282.30
7 purchase totals =	$1,039.48		$1,133.6491	$1,133.65	$1,133.70	$1,133.60