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	$120.96	8.546%	$131.2972	$131.30	$131.30	$131.30
Purchase #2	$68.36	5.742%	$72.2852	$72.29	$72.30	$72.30
Purchase #3	$123.82	8.699%	$134.5911	$134.59	$134.60	$134.60
Purchase #4	$10.98	10.489%	$12.1317	$12.13	$12.15	$12.10
Purchase #5	$167.54	10.184%	$184.6023	$184.60	$184.60	$184.60
Purchase #6	$193.77	9.608%	$212.3874	$212.39	$212.40	$212.40
Purchase #7	$45.92	12.280%	$51.559	$51.56	$51.55	$51.60
7 purchase totals =	$731.35		$798.8539	$798.86	$798.90	$798.90