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	$122.67	13.836%	$139.6426	$139.64	$139.65	$139.60
Purchase #2	$141.79	6.190%	$150.5668	$150.57	$150.55	$150.60
Purchase #3	$75.99	11.250%	$84.5389	$84.54	$84.55	$84.50
Purchase #4	$233.38	6.690%	$248.9931	$248.99	$249.00	$249.00
Purchase #5	$97.92	13.581%	$111.2185	$111.22	$111.20	$111.20
Purchase #6	$91.95	8.225%	$99.5129	$99.51	$99.50	$99.50
Purchase #7	$178.61	3.406%	$184.6935	$184.69	$184.70	$184.70
7 purchase totals =	$942.31		$1,019.1663	$1,019.16	$1,019.15	$1,019.10