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	$241.27	3.667%	$250.1174	$250.12	$250.10	$250.10
Purchase #2	$225.33	9.157%	$245.9635	$245.96	$245.95	$246.00
Purchase #3	$88.59	13.789%	$100.8057	$100.81	$100.80	$100.80
Purchase #4	$46.80	13.825%	$53.2701	$53.27	$53.25	$53.30
Purchase #5	$241.52	13.159%	$273.3016	$273.30	$273.30	$273.30
Purchase #6	$78.80	5.588%	$83.2033	$83.20	$83.20	$83.20
Purchase #7	$249.71	3.426%	$258.2651	$258.27	$258.25	$258.30
7 purchase totals =	$1,172.02		$1,264.9267	$1,264.93	$1,264.85	$1,265.00