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	$230.57	10.264%	$254.2357	$254.24	$254.25	$254.20
Purchase #2	$154.58	3.243%	$159.593	$159.59	$159.60	$159.60
Purchase #3	$99.59	5.258%	$104.8264	$104.83	$104.85	$104.80
Purchase #4	$156.31	8.625%	$169.7917	$169.79	$169.80	$169.80
Purchase #5	$227.81	5.487%	$240.3099	$240.31	$240.30	$240.30
Purchase #6	$105.62	9.678%	$115.8419	$115.84	$115.85	$115.80
Purchase #7	$37.99	10.299%	$41.9026	$41.90	$41.90	$41.90
7 purchase totals =	$1,012.47		$1,086.5012	$1,086.50	$1,086.55	$1,086.40