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	$115.83	4.722%	$121.2995	$121.30	$121.30	$121.30
Purchase #2	$205.49	6.377%	$218.5941	$218.59	$218.60	$218.60
Purchase #3	$179.38	6.179%	$190.4639	$190.46	$190.45	$190.50
Purchase #4	$37.92	10.617%	$41.946	$41.95	$41.95	$41.90
Purchase #5	$145.69	4.438%	$152.1557	$152.16	$152.15	$152.20
Purchase #6	$233.63	9.105%	$254.902	$254.90	$254.90	$254.90
Purchase #7	$229.55	9.549%	$251.4697	$251.47	$251.45	$251.50
7 purchase totals =	$1,147.49		$1,230.8309	$1,230.83	$1,230.80	$1,230.90