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	$159.89	12.805%	$180.3639	$180.36	$180.35	$180.40
Purchase #2	$128.37	8.398%	$139.1505	$139.15	$139.15	$139.20
Purchase #3	$135.93	13.519%	$154.3064	$154.31	$154.30	$154.30
Purchase #4	$151.52	3.658%	$157.0626	$157.06	$157.05	$157.10
Purchase #5	$248.95	8.539%	$270.2078	$270.21	$270.20	$270.20
Purchase #6	$37.89	9.423%	$41.4604	$41.46	$41.45	$41.50
Purchase #7	$142.87	6.739%	$152.498	$152.50	$152.50	$152.50
7 purchase totals =	$1,005.42		$1,095.0496	$1,095.05	$1,095.00	$1,095.20