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	$72.45	7.733%	$78.0526	$78.05	$78.05	$78.10
Purchase #2	$57.47	11.471%	$64.0624	$64.06	$64.05	$64.10
Purchase #3	$158.81	12.342%	$178.4103	$178.41	$178.40	$178.40
Purchase #4	$132.89	10.811%	$147.2567	$147.26	$147.25	$147.30
Purchase #5	$165.63	4.368%	$172.8647	$172.86	$172.85	$172.90
Purchase #6	$245.91	12.116%	$275.7045	$275.70	$275.70	$275.70
Purchase #7	$47.37	11.196%	$52.6735	$52.67	$52.65	$52.70
7 purchase totals =	$880.53		$969.0247	$969.01	$968.95	$969.20