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	$226.99	7.219%	$243.3764	$243.38	$243.40	$243.40
Purchase #2	$55.52	4.105%	$57.7991	$57.80	$57.80	$57.80
Purchase #3	$78.77	13.603%	$89.4851	$89.49	$89.50	$89.50
Purchase #4	$210.98	3.474%	$218.3094	$218.31	$218.30	$218.30
Purchase #5	$175.50	10.766%	$194.3943	$194.39	$194.40	$194.40
Purchase #6	$131.50	6.218%	$139.6767	$139.68	$139.70	$139.70
Purchase #7	$7.67	9.515%	$8.3998	$8.40	$8.40	$8.40
7 purchase totals =	$886.93		$951.4408	$951.45	$951.50	$951.50