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	$93.88	5.449%	$98.9955	$99.00	$99.00	$99.00
Purchase #2	$122.78	13.319%	$139.1331	$139.13	$139.15	$139.10
Purchase #3	$181.99	10.387%	$200.8933	$200.89	$200.90	$200.90
Purchase #4	$156.25	12.163%	$175.2547	$175.25	$175.25	$175.30
Purchase #5	$62.34	7.324%	$66.9058	$66.91	$66.90	$66.90
Purchase #6	$32.85	6.817%	$35.0894	$35.09	$35.10	$35.10
Purchase #7	$122.63	7.564%	$131.9057	$131.91	$131.90	$131.90
7 purchase totals =	$772.72		$848.1775	$848.18	$848.20	$848.20