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	$232.45	3.693%	$241.0344	$241.03	$241.05	$241.00
Purchase #2	$97.45	11.414%	$108.5729	$108.57	$108.55	$108.60
Purchase #3	$234.53	8.472%	$254.3994	$254.40	$254.40	$254.40
Purchase #4	$174.73	9.671%	$191.6281	$191.63	$191.65	$191.60
Purchase #5	$90.30	13.415%	$102.4137	$102.41	$102.40	$102.40
Purchase #6	$72.41	11.302%	$80.5938	$80.59	$80.60	$80.60
Purchase #7	$22.47	12.665%	$25.3158	$25.32	$25.30	$25.30
7 purchase totals =	$924.34		$1,003.9581	$1,003.95	$1,003.95	$1,003.90