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	$111.44	10.868%	$123.5513	$123.55	$123.55	$123.60
Purchase #2	$206.58	11.296%	$229.9153	$229.92	$229.90	$229.90
Purchase #3	$159.87	8.416%	$173.3247	$173.32	$173.30	$173.30
Purchase #4	$88.86	13.347%	$100.7201	$100.72	$100.70	$100.70
Purchase #5	$110.30	3.559%	$114.2256	$114.23	$114.25	$114.20
Purchase #6	$35.31	7.807%	$38.0667	$38.07	$38.05	$38.10
Purchase #7	$26.44	8.558%	$28.7027	$28.70	$28.70	$28.70
7 purchase totals =	$738.80		$808.5064	$808.51	$808.45	$808.50