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	$139.29	5.590%	$147.0763	$147.08	$147.10	$147.10
Purchase #2	$62.28	11.256%	$69.2902	$69.29	$69.30	$69.30
Purchase #3	$98.27	10.817%	$108.8999	$108.90	$108.90	$108.90
Purchase #4	$138.46	12.734%	$156.0915	$156.09	$156.10	$156.10
Purchase #5	$203.56	5.406%	$214.5645	$214.56	$214.55	$214.60
Purchase #6	$89.85	7.870%	$96.9212	$96.92	$96.90	$96.90
Purchase #7	$186.98	12.613%	$210.5638	$210.56	$210.55	$210.60
7 purchase totals =	$918.69		$1,003.4074	$1,003.40	$1,003.40	$1,003.50