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	$83.78	7.333%	$89.9236	$89.92	$89.90	$89.90
Purchase #2	$224.75	5.587%	$237.3068	$237.31	$237.30	$237.30
Purchase #3	$52.90	8.741%	$57.524	$57.52	$57.50	$57.50
Purchase #4	$167.59	6.714%	$178.842	$178.84	$178.85	$178.80
Purchase #5	$81.26	7.536%	$87.3838	$87.38	$87.40	$87.40
Purchase #6	$37.97	7.654%	$40.8762	$40.88	$40.90	$40.90
Purchase #7	$227.76	13.849%	$259.3025	$259.30	$259.30	$259.30
7 purchase totals =	$876.01		$951.1589	$951.15	$951.15	$951.10