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	$48.29	8.779%	$52.5294	$52.53	$52.55	$52.50
Purchase #2	$151.51	10.104%	$166.8186	$166.82	$166.80	$166.80
Purchase #3	$178.92	3.627%	$185.4094	$185.41	$185.40	$185.40
Purchase #4	$230.52	8.725%	$250.6329	$250.63	$250.65	$250.60
Purchase #5	$235.34	5.179%	$247.5283	$247.53	$247.55	$247.50
Purchase #6	$179.74	8.119%	$194.3331	$194.33	$194.35	$194.30
Purchase #7	$164.72	12.524%	$185.3495	$185.35	$185.35	$185.30
7 purchase totals =	$1,189.04		$1,282.6012	$1,282.60	$1,282.65	$1,282.40