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	$84.79	4.804%	$88.8633	$88.86	$88.85	$88.90
Purchase #2	$127.60	9.191%	$139.3277	$139.33	$139.35	$139.30
Purchase #3	$95.47	6.700%	$101.8665	$101.87	$101.85	$101.90
Purchase #4	$38.91	10.169%	$42.8668	$42.87	$42.85	$42.90
Purchase #5	$39.66	8.593%	$43.068	$43.07	$43.05	$43.10
Purchase #6	$42.76	8.546%	$46.4143	$46.41	$46.40	$46.40
Purchase #7	$130.41	8.610%	$141.6383	$141.64	$141.65	$141.60
7 purchase totals =	$559.60		$604.0449	$604.05	$604.00	$604.10