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	$14.35	7.483%	$15.4238	$15.42	$15.40	$15.40
Purchase #2	$210.50	11.508%	$234.7243	$234.72	$234.70	$234.70
Purchase #3	$78.83	4.189%	$82.1322	$82.13	$82.15	$82.10
Purchase #4	$180.86	12.520%	$203.5037	$203.50	$203.50	$203.50
Purchase #5	$82.31	11.749%	$91.9806	$91.98	$92.00	$92.00
Purchase #6	$118.83	10.148%	$130.8889	$130.89	$130.90	$130.90
Purchase #7	$233.35	6.406%	$248.2984	$248.30	$248.30	$248.30
7 purchase totals =	$919.03		$1,006.9519	$1,006.94	$1,006.95	$1,006.90