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	$10.43	9.372%	$11.4075	$11.41	$11.40	$11.40
Purchase #2	$165.52	13.865%	$188.4693	$188.47	$188.45	$188.50
Purchase #3	$160.39	12.498%	$180.4355	$180.44	$180.45	$180.40
Purchase #4	$151.76	6.355%	$161.4043	$161.40	$161.40	$161.40
Purchase #5	$34.79	8.398%	$37.7117	$37.71	$37.70	$37.70
Purchase #6	$52.83	12.803%	$59.5938	$59.59	$59.60	$59.60
Purchase #7	$234.63	7.207%	$251.5398	$251.54	$251.55	$251.50
7 purchase totals =	$810.35		$890.5619	$890.56	$890.55	$890.50