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	$7.37	5.223%	$7.7549	$7.75	$7.75	$7.80
Purchase #2	$245.78	10.613%	$271.8646	$271.86	$271.85	$271.90
Purchase #3	$74.31	5.802%	$78.6215	$78.62	$78.60	$78.60
Purchase #4	$241.58	11.454%	$269.2506	$269.25	$269.25	$269.30
Purchase #5	$35.71	10.515%	$39.4649	$39.46	$39.45	$39.50
Purchase #6	$234.65	11.288%	$261.1373	$261.14	$261.15	$261.10
Purchase #7	$248.88	13.228%	$281.8018	$281.80	$281.80	$281.80
7 purchase totals =	$1,088.28		$1,209.8956	$1,209.88	$1,209.85	$1,210.00