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	$6.98	13.515%	$7.9233	$7.92	$7.90	$7.90
Purchase #2	$62.29	7.599%	$67.0234	$67.02	$67.00	$67.00
Purchase #3	$9.77	11.640%	$10.9072	$10.91	$10.90	$10.90
Purchase #4	$51.30	12.106%	$57.5104	$57.51	$57.50	$57.50
Purchase #5	$177.70	10.809%	$196.9076	$196.91	$196.90	$196.90
Purchase #6	$234.39	7.235%	$251.3481	$251.35	$251.35	$251.30
Purchase #7	$219.28	3.780%	$227.5688	$227.57	$227.55	$227.60
7 purchase totals =	$761.71		$819.1888	$819.19	$819.10	$819.10