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	$69.37	11.418%	$77.2907	$77.29	$77.30	$77.30
Purchase #2	$250.40	8.252%	$271.063	$271.06	$271.05	$271.10
Purchase #3	$165.61	12.592%	$186.4636	$186.46	$186.45	$186.50
Purchase #4	$17.79	8.192%	$19.2474	$19.25	$19.25	$19.20
Purchase #5	$215.67	11.683%	$240.8667	$240.87	$240.85	$240.90
Purchase #6	$199.81	4.314%	$208.4298	$208.43	$208.45	$208.40
Purchase #7	$123.76	3.223%	$127.7488	$127.75	$127.75	$127.70
7 purchase totals =	$1,042.41		$1,131.1100	$1,131.11	$1,131.10	$1,131.10