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	$38.28	11.383%	$42.6374	$42.64	$42.65	$42.60
Purchase #2	$168.66	10.601%	$186.5396	$186.54	$186.55	$186.50
Purchase #3	$155.39	3.316%	$160.5427	$160.54	$160.55	$160.50
Purchase #4	$207.49	4.425%	$216.6714	$216.67	$216.65	$216.70
Purchase #5	$205.52	3.531%	$212.7769	$212.78	$212.80	$212.80
Purchase #6	$39.31	8.870%	$42.7968	$42.80	$42.80	$42.80
Purchase #7	$133.41	13.432%	$151.3296	$151.33	$151.35	$151.30
7 purchase totals =	$948.06		$1,013.2944	$1,013.30	$1,013.35	$1,013.20