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	$85.51	3.588%	$88.5781	$88.58	$88.60	$88.60
Purchase #2	$5.82	9.623%	$6.3801	$6.38	$6.40	$6.40
Purchase #3	$53.80	11.429%	$59.9488	$59.95	$59.95	$59.90
Purchase #4	$156.28	11.694%	$174.5554	$174.56	$174.55	$174.60
Purchase #5	$75.86	11.808%	$84.8175	$84.82	$84.80	$84.80
Purchase #6	$42.58	4.297%	$44.4097	$44.41	$44.40	$44.40
Purchase #7	$94.33	6.242%	$100.2181	$100.22	$100.20	$100.20
7 purchase totals =	$514.18		$558.9077	$558.92	$558.90	$558.90