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	$192.69	5.755%	$203.7793	$203.78	$203.80	$203.80
Purchase #2	$110.44	3.761%	$114.5936	$114.59	$114.60	$114.60
Purchase #3	$221.25	12.620%	$249.1718	$249.17	$249.15	$249.20
Purchase #4	$190.35	11.672%	$212.5677	$212.57	$212.55	$212.60
Purchase #5	$111.83	4.521%	$116.8858	$116.89	$116.90	$116.90
Purchase #6	$150.95	10.552%	$166.8782	$166.88	$166.90	$166.90
Purchase #7	$18.37	9.418%	$20.1001	$20.10	$20.10	$20.10
7 purchase totals =	$995.88		$1,083.9765	$1,083.98	$1,084.00	$1,084.10