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	$132.43	9.734%	$145.3207	$145.32	$145.30	$145.30
Purchase #2	$41.65	12.257%	$46.755	$46.76	$46.75	$46.80
Purchase #3	$23.72	3.369%	$24.5191	$24.52	$24.50	$24.50
Purchase #4	$51.59	7.331%	$55.3721	$55.37	$55.35	$55.40
Purchase #5	$64.63	12.850%	$72.935	$72.94	$72.95	$72.90
Purchase #6	$41.82	10.764%	$46.3215	$46.32	$46.30	$46.30
Purchase #7	$180.52	6.251%	$191.8043	$191.80	$191.80	$191.80
7 purchase totals =	$536.36		$583.0277	$583.03	$582.95	$583.00