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	$35.27	13.167%	$39.914	$39.91	$39.90	$39.90
Purchase #2	$180.27	5.406%	$190.0154	$190.02	$190.00	$190.00
Purchase #3	$250.34	13.870%	$285.0622	$285.06	$285.05	$285.10
Purchase #4	$54.81	8.116%	$59.2584	$59.26	$59.25	$59.30
Purchase #5	$134.89	12.543%	$151.8093	$151.81	$151.80	$151.80
Purchase #6	$239.67	11.658%	$267.6107	$267.61	$267.60	$267.60
Purchase #7	$29.57	8.348%	$32.0385	$32.04	$32.05	$32.00
7 purchase totals =	$924.82		$1,025.7085	$1,025.71	$1,025.65	$1,025.70