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	$88.74	6.659%	$94.6492	$94.65	$94.65	$94.60
Purchase #2	$124.87	6.776%	$133.3312	$133.33	$133.35	$133.30
Purchase #3	$88.82	12.873%	$100.2538	$100.25	$100.25	$100.30
Purchase #4	$35.86	6.462%	$38.1773	$38.18	$38.20	$38.20
Purchase #5	$112.26	11.610%	$125.2934	$125.29	$125.30	$125.30
Purchase #6	$71.52	4.665%	$74.8564	$74.86	$74.85	$74.90
Purchase #7	$89.51	12.673%	$100.8536	$100.85	$100.85	$100.90
7 purchase totals =	$611.58		$667.4149	$667.41	$667.45	$667.50