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	$176.80	3.287%	$182.6114	$182.61	$182.60	$182.60
Purchase #2	$67.33	6.519%	$71.7192	$71.72	$71.70	$71.70
Purchase #3	$43.89	10.687%	$48.5805	$48.58	$48.60	$48.60
Purchase #4	$144.27	10.213%	$159.0043	$159.00	$159.00	$159.00
Purchase #5	$217.96	12.404%	$244.9958	$245.00	$245.00	$245.00
Purchase #6	$31.93	4.318%	$33.3087	$33.31	$33.30	$33.30
Purchase #7	$56.33	7.641%	$60.6342	$60.63	$60.65	$60.60
7 purchase totals =	$738.51		$800.8541	$800.85	$800.85	$800.80