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	$236.65	13.391%	$268.3398	$268.34	$268.35	$268.30
Purchase #2	$143.59	5.821%	$151.9484	$151.95	$151.95	$151.90
Purchase #3	$16.27	7.149%	$17.4331	$17.43	$17.45	$17.40
Purchase #4	$93.80	7.283%	$100.6315	$100.63	$100.65	$100.60
Purchase #5	$128.79	12.474%	$144.8553	$144.86	$144.85	$144.90
Purchase #6	$250.36	12.402%	$281.4096	$281.41	$281.40	$281.40
Purchase #7	$47.37	11.156%	$52.6546	$52.65	$52.65	$52.70
7 purchase totals =	$916.83		$1,017.2723	$1,017.27	$1,017.30	$1,017.20