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	$17.63	9.339%	$19.2765	$19.28	$19.30	$19.30
Purchase #2	$39.27	4.419%	$41.0053	$41.01	$41.00	$41.00
Purchase #3	$191.33	9.385%	$209.2863	$209.29	$209.30	$209.30
Purchase #4	$237.64	13.554%	$269.8497	$269.85	$269.85	$269.80
Purchase #5	$59.99	12.673%	$67.5925	$67.59	$67.60	$67.60
Purchase #6	$55.39	4.390%	$57.8216	$57.82	$57.80	$57.80
Purchase #7	$41.76	12.259%	$46.8794	$46.88	$46.90	$46.90
7 purchase totals =	$643.01		$711.7113	$711.72	$711.75	$711.70