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	$44.65	12.703%	$50.3219	$50.32	$50.30	$50.30
Purchase #2	$197.40	11.588%	$220.2747	$220.27	$220.25	$220.30
Purchase #3	$138.94	10.721%	$153.8358	$153.84	$153.85	$153.80
Purchase #4	$212.25	3.144%	$218.9231	$218.92	$218.90	$218.90
Purchase #5	$168.26	13.780%	$191.4462	$191.45	$191.45	$191.40
Purchase #6	$38.39	7.627%	$41.318	$41.32	$41.30	$41.30
Purchase #7	$97.43	5.111%	$102.4096	$102.41	$102.40	$102.40
7 purchase totals =	$897.32		$978.5293	$978.53	$978.45	$978.40