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	$155.43	8.573%	$168.755	$168.76	$168.75	$168.80
Purchase #2	$134.73	12.179%	$151.1388	$151.14	$151.15	$151.10
Purchase #3	$173.69	4.286%	$181.1344	$181.13	$181.15	$181.10
Purchase #4	$232.64	11.670%	$259.7891	$259.79	$259.80	$259.80
Purchase #5	$45.46	11.719%	$50.7875	$50.79	$50.80	$50.80
Purchase #6	$64.32	11.331%	$71.6081	$71.61	$71.60	$71.60
Purchase #7	$92.48	8.811%	$100.6284	$100.63	$100.65	$100.60
7 purchase totals =	$898.75		$983.8413	$983.85	$983.90	$983.80