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	$32.39	10.798%	$35.8875	$35.89	$35.90	$35.90
Purchase #2	$155.26	13.447%	$176.1378	$176.14	$176.15	$176.10
Purchase #3	$90.87	3.585%	$94.1277	$94.13	$94.15	$94.10
Purchase #4	$88.58	12.566%	$99.711	$99.71	$99.70	$99.70
Purchase #5	$170.55	9.589%	$186.904	$186.90	$186.90	$186.90
Purchase #6	$224.69	9.492%	$246.0176	$246.02	$246.00	$246.00
Purchase #7	$82.91	9.421%	$90.721	$90.72	$90.70	$90.70
7 purchase totals =	$845.25		$929.5066	$929.51	$929.50	$929.40