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	$250.39	3.306%	$258.6679	$258.67	$258.65	$258.70
Purchase #2	$127.70	10.614%	$141.2541	$141.25	$141.25	$141.30
Purchase #3	$29.59	12.870%	$33.3982	$33.40	$33.40	$33.40
Purchase #4	$146.54	5.285%	$154.2846	$154.28	$154.30	$154.30
Purchase #5	$237.69	11.330%	$264.6203	$264.62	$264.60	$264.60
Purchase #6	$46.67	13.512%	$52.9761	$52.98	$53.00	$53.00
Purchase #7	$86.37	10.795%	$95.6936	$95.69	$95.70	$95.70
7 purchase totals =	$924.95		$1,000.8948	$1,000.89	$1,000.90	$1,001.00