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	$144.26	6.862%	$154.1591	$154.16	$154.15	$154.20
Purchase #2	$222.90	11.398%	$248.3061	$248.31	$248.30	$248.30
Purchase #3	$102.45	3.352%	$105.8841	$105.88	$105.90	$105.90
Purchase #4	$133.42	7.305%	$143.1663	$143.17	$143.15	$143.20
Purchase #5	$17.97	8.813%	$19.5537	$19.55	$19.55	$19.60
Purchase #6	$75.95	12.130%	$85.1627	$85.16	$85.15	$85.20
Purchase #7	$73.91	12.260%	$82.9714	$82.97	$82.95	$83.00
7 purchase totals =	$770.86		$839.2034	$839.20	$839.15	$839.40