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	$129.32	12.417%	$145.3777	$145.38	$145.40	$145.40
Purchase #2	$61.76	8.559%	$67.046	$67.05	$67.05	$67.00
Purchase #3	$185.76	13.611%	$211.0438	$211.04	$211.05	$211.00
Purchase #4	$25.42	9.113%	$27.7365	$27.74	$27.75	$27.70
Purchase #5	$31.92	8.160%	$34.5247	$34.52	$34.50	$34.50
Purchase #6	$36.46	4.336%	$38.0409	$38.04	$38.05	$38.00
Purchase #7	$136.59	5.361%	$143.9126	$143.91	$143.90	$143.90
7 purchase totals =	$607.23		$667.6822	$667.68	$667.70	$667.50