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	$66.42	9.761%	$72.9033	$72.90	$72.90	$72.90
Purchase #2	$178.82	8.413%	$193.8641	$193.86	$193.85	$193.90
Purchase #3	$17.77	9.175%	$19.4004	$19.40	$19.40	$19.40
Purchase #4	$233.77	8.614%	$253.9069	$253.91	$253.90	$253.90
Purchase #5	$144.48	7.493%	$155.3059	$155.31	$155.30	$155.30
Purchase #6	$135.69	11.676%	$151.5332	$151.53	$151.55	$151.50
Purchase #7	$46.78	7.140%	$50.1201	$50.12	$50.10	$50.10
7 purchase totals =	$823.73		$897.0339	$897.03	$897.00	$897.00