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	$19.78	7.721%	$21.3072	$21.31	$21.30	$21.30
Purchase #2	$210.82	10.762%	$233.5084	$233.51	$233.50	$233.50
Purchase #3	$140.69	3.731%	$145.9391	$145.94	$145.95	$145.90
Purchase #4	$69.96	7.212%	$75.0055	$75.01	$75.00	$75.00
Purchase #5	$99.78	8.775%	$108.5357	$108.54	$108.55	$108.50
Purchase #6	$248.46	6.625%	$264.9205	$264.92	$264.90	$264.90
Purchase #7	$199.52	4.486%	$208.4705	$208.47	$208.45	$208.50
7 purchase totals =	$989.01		$1,057.6869	$1,057.70	$1,057.65	$1,057.60