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	$46.41	6.266%	$49.3181	$49.32	$49.30	$49.30
Purchase #2	$198.40	13.511%	$225.2058	$225.21	$225.20	$225.20
Purchase #3	$46.57	13.685%	$52.9431	$52.94	$52.95	$52.90
Purchase #4	$230.59	12.219%	$258.7658	$258.77	$258.75	$258.80
Purchase #5	$76.69	11.174%	$85.2593	$85.26	$85.25	$85.30
Purchase #6	$142.84	7.491%	$153.5401	$153.54	$153.55	$153.50
Purchase #7	$76.37	9.356%	$83.5152	$83.52	$83.50	$83.50
7 purchase totals =	$817.87		$908.5474	$908.56	$908.50	$908.50