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	$28.75	10.539%	$31.78	$31.78	$31.80	$31.80
Purchase #2	$242.55	11.661%	$270.8338	$270.83	$270.85	$270.80
Purchase #3	$88.61	13.323%	$100.4155	$100.42	$100.40	$100.40
Purchase #4	$205.31	6.576%	$218.8112	$218.81	$218.80	$218.80
Purchase #5	$228.76	10.303%	$252.3291	$252.33	$252.35	$252.30
Purchase #6	$39.48	13.191%	$44.6878	$44.69	$44.70	$44.70
Purchase #7	$117.46	5.398%	$123.8005	$123.80	$123.80	$123.80
7 purchase totals =	$950.92		$1,042.6579	$1,042.66	$1,042.70	$1,042.60