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	$69.80	12.284%	$78.3742	$78.37	$78.35	$78.40
Purchase #2	$239.94	9.513%	$262.7655	$262.77	$262.75	$262.80
Purchase #3	$117.39	11.368%	$130.7349	$130.73	$130.75	$130.70
Purchase #4	$118.77	7.557%	$127.7454	$127.75	$127.75	$127.70
Purchase #5	$132.46	10.245%	$146.0305	$146.03	$146.05	$146.00
Purchase #6	$94.56	9.358%	$103.4089	$103.41	$103.40	$103.40
Purchase #7	$247.62	7.373%	$265.877	$265.88	$265.90	$265.90
7 purchase totals =	$1,020.54		$1,114.9364	$1,114.94	$1,114.95	$1,114.90