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	$26.93	5.389%	$28.3813	$28.38	$28.40	$28.40
Purchase #2	$46.98	6.787%	$50.1685	$50.17	$50.15	$50.20
Purchase #3	$224.78	13.259%	$254.5836	$254.58	$254.60	$254.60
Purchase #4	$208.57	11.850%	$233.2855	$233.29	$233.30	$233.30
Purchase #5	$7.89	6.464%	$8.4	$8.40	$8.40	$8.40
Purchase #6	$214.32	9.330%	$234.3161	$234.32	$234.30	$234.30
Purchase #7	$184.89	8.270%	$200.1804	$200.18	$200.20	$200.20
7 purchase totals =	$914.36		$1,009.3154	$1,009.32	$1,009.35	$1,009.40