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	$166.25	7.535%	$178.7769	$178.78	$178.80	$178.80
Purchase #2	$64.44	11.759%	$72.0175	$72.02	$72.00	$72.00
Purchase #3	$196.30	9.600%	$215.1448	$215.14	$215.15	$215.10
Purchase #4	$64.91	10.546%	$71.7554	$71.76	$71.75	$71.80
Purchase #5	$18.78	12.366%	$21.1023	$21.10	$21.10	$21.10
Purchase #6	$111.88	3.778%	$116.1068	$116.11	$116.10	$116.10
Purchase #7	$126.44	13.263%	$143.2097	$143.21	$143.20	$143.20
7 purchase totals =	$749.00		$818.1134	$818.12	$818.10	$818.10