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	$217.77	5.568%	$229.8954	$229.90	$229.90	$229.90
Purchase #2	$53.44	3.228%	$55.165	$55.17	$55.15	$55.20
Purchase #3	$147.57	12.364%	$165.8156	$165.82	$165.80	$165.80
Purchase #4	$142.45	9.870%	$156.5098	$156.51	$156.50	$156.50
Purchase #5	$210.75	12.197%	$236.4552	$236.46	$236.45	$236.50
Purchase #6	$44.62	9.399%	$48.8138	$48.81	$48.80	$48.80
Purchase #7	$52.41	4.202%	$54.6123	$54.61	$54.60	$54.60
7 purchase totals =	$869.01		$947.2671	$947.28	$947.20	$947.30