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	$37.93	10.220%	$41.8064	$41.81	$41.80	$41.80
Purchase #2	$127.64	4.589%	$133.4974	$133.50	$133.50	$133.50
Purchase #3	$79.47	12.482%	$89.3894	$89.39	$89.40	$89.40
Purchase #4	$236.30	5.313%	$248.8546	$248.85	$248.85	$248.90
Purchase #5	$38.61	10.108%	$42.5127	$42.51	$42.50	$42.50
Purchase #6	$65.36	7.663%	$70.3685	$70.37	$70.35	$70.40
Purchase #7	$138.95	5.661%	$146.816	$146.82	$146.80	$146.80
7 purchase totals =	$724.26		$773.2450	$773.25	$773.20	$773.30