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	$166.58	10.661%	$184.3391	$184.34	$184.35	$184.30
Purchase #2	$159.56	12.758%	$179.9167	$179.92	$179.90	$179.90
Purchase #3	$156.28	5.821%	$165.3771	$165.38	$165.40	$165.40
Purchase #4	$103.63	9.144%	$113.1059	$113.11	$113.10	$113.10
Purchase #5	$167.47	6.118%	$177.7158	$177.72	$177.70	$177.70
Purchase #6	$222.37	8.332%	$240.8979	$240.90	$240.90	$240.90
Purchase #7	$123.89	9.339%	$135.4601	$135.46	$135.45	$135.50
7 purchase totals =	$1,099.78		$1,196.8126	$1,196.83	$1,196.80	$1,196.80