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	$74.93	3.171%	$77.306	$77.31	$77.30	$77.30
Purchase #2	$248.30	8.626%	$269.7184	$269.72	$269.70	$269.70
Purchase #3	$238.48	8.772%	$259.3995	$259.40	$259.40	$259.40
Purchase #4	$136.57	7.541%	$146.8687	$146.87	$146.85	$146.90
Purchase #5	$144.36	10.514%	$159.538	$159.54	$159.55	$159.50
Purchase #6	$85.48	4.490%	$89.3181	$89.32	$89.30	$89.30
Purchase #7	$134.78	3.414%	$139.3814	$139.38	$139.40	$139.40
7 purchase totals =	$1,062.90		$1,141.5301	$1,141.54	$1,141.50	$1,141.50