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	$172.49	10.302%	$190.2599	$190.26	$190.25	$190.30
Purchase #2	$86.51	3.198%	$89.2766	$89.28	$89.30	$89.30
Purchase #3	$127.38	12.802%	$143.6872	$143.69	$143.70	$143.70
Purchase #4	$57.89	9.752%	$63.5354	$63.54	$63.55	$63.50
Purchase #5	$61.27	12.857%	$69.1475	$69.15	$69.15	$69.10
Purchase #6	$230.98	7.354%	$247.9663	$247.97	$247.95	$248.00
Purchase #7	$169.56	6.188%	$180.0524	$180.05	$180.05	$180.10
7 purchase totals =	$906.08		$983.9253	$983.94	$983.95	$984.00