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	$238.89	10.435%	$263.8182	$263.82	$263.80	$263.80
Purchase #2	$149.63	7.515%	$160.8747	$160.87	$160.85	$160.90
Purchase #3	$103.80	7.229%	$111.3037	$111.30	$111.30	$111.30
Purchase #4	$164.68	6.705%	$175.7218	$175.72	$175.70	$175.70
Purchase #5	$160.54	5.143%	$168.7966	$168.80	$168.80	$168.80
Purchase #6	$120.88	12.372%	$135.8353	$135.84	$135.85	$135.80
Purchase #7	$45.82	12.715%	$51.646	$51.65	$51.65	$51.60
7 purchase totals =	$984.24		$1,067.9963	$1,068.00	$1,067.95	$1,067.90