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	$189.61	13.501%	$215.2092	$215.21	$215.20	$215.20
Purchase #2	$163.36	9.769%	$179.3186	$179.32	$179.30	$179.30
Purchase #3	$48.25	12.614%	$54.3363	$54.34	$54.35	$54.30
Purchase #4	$171.36	11.870%	$191.7004	$191.70	$191.70	$191.70
Purchase #5	$199.82	7.680%	$215.1662	$215.17	$215.15	$215.20
Purchase #6	$62.53	12.429%	$70.3019	$70.30	$70.30	$70.30
Purchase #7	$134.37	7.566%	$144.5364	$144.54	$144.55	$144.50
7 purchase totals =	$969.30		$1,070.5690	$1,070.58	$1,070.55	$1,070.50