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	$91.57	8.353%	$99.2188	$99.22	$99.20	$99.20
Purchase #2	$97.63	12.207%	$109.5477	$109.55	$109.55	$109.50
Purchase #3	$102.53	5.661%	$108.3342	$108.33	$108.35	$108.30
Purchase #4	$167.50	10.276%	$184.7123	$184.71	$184.70	$184.70
Purchase #5	$127.90	6.113%	$135.7185	$135.72	$135.70	$135.70
Purchase #6	$196.42	11.607%	$219.2185	$219.22	$219.20	$219.20
Purchase #7	$120.79	3.388%	$124.8824	$124.88	$124.90	$124.90
7 purchase totals =	$904.34		$981.6324	$981.63	$981.60	$981.50