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	$143.89	4.262%	$150.0226	$150.02	$150.00	$150.00
Purchase #2	$20.99	3.261%	$21.6745	$21.67	$21.65	$21.70
Purchase #3	$119.71	3.109%	$123.4318	$123.43	$123.45	$123.40
Purchase #4	$25.46	6.343%	$27.0749	$27.07	$27.05	$27.10
Purchase #5	$97.53	13.789%	$110.9784	$110.98	$111.00	$111.00
Purchase #6	$79.34	10.561%	$87.7191	$87.72	$87.70	$87.70
Purchase #7	$113.97	3.727%	$118.2177	$118.22	$118.20	$118.20
7 purchase totals =	$600.89		$639.1190	$639.11	$639.05	$639.10