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	$118.59	4.657%	$124.1127	$124.11	$124.10	$124.10
Purchase #2	$196.41	10.382%	$216.8013	$216.80	$216.80	$216.80
Purchase #3	$107.59	7.191%	$115.3268	$115.33	$115.35	$115.30
Purchase #4	$186.41	5.158%	$196.025	$196.03	$196.05	$196.00
Purchase #5	$94.67	4.815%	$99.2284	$99.23	$99.25	$99.20
Purchase #6	$55.80	9.467%	$61.0826	$61.08	$61.10	$61.10
Purchase #7	$127.49	12.824%	$143.8393	$143.84	$143.85	$143.80
7 purchase totals =	$886.96		$956.4161	$956.42	$956.50	$956.30