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	$82.31	10.123%	$90.6422	$90.64	$90.65	$90.60
Purchase #2	$242.28	10.599%	$267.9593	$267.96	$267.95	$268.00
Purchase #3	$57.55	4.736%	$60.2756	$60.28	$60.30	$60.30
Purchase #4	$31.90	6.309%	$33.9126	$33.91	$33.90	$33.90
Purchase #5	$13.98	9.552%	$15.3154	$15.32	$15.30	$15.30
Purchase #6	$181.50	13.164%	$205.3927	$205.39	$205.40	$205.40
Purchase #7	$150.70	3.707%	$156.2864	$156.29	$156.30	$156.30
7 purchase totals =	$760.22		$829.7842	$829.79	$829.80	$829.80