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	$25.30	13.679%	$28.7608	$28.76	$28.75	$28.80
Purchase #2	$198.72	11.872%	$222.312	$222.31	$222.30	$222.30
Purchase #3	$23.89	4.125%	$24.8755	$24.88	$24.90	$24.90
Purchase #4	$223.71	4.502%	$233.7814	$233.78	$233.80	$233.80
Purchase #5	$43.93	11.837%	$49.13	$49.13	$49.15	$49.10
Purchase #6	$125.51	7.378%	$134.7701	$134.77	$134.75	$134.80
Purchase #7	$235.41	7.834%	$253.852	$253.85	$253.85	$253.90
7 purchase totals =	$876.47		$947.4818	$947.48	$947.50	$947.60