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	$96.34	3.666%	$99.8718	$99.87	$99.85	$99.90
Purchase #2	$150.35	12.691%	$169.4309	$169.43	$169.45	$169.40
Purchase #3	$103.96	4.132%	$108.2556	$108.26	$108.25	$108.30
Purchase #4	$244.98	3.696%	$254.0345	$254.03	$254.05	$254.00
Purchase #5	$40.29	4.687%	$42.1784	$42.18	$42.20	$42.20
Purchase #6	$182.44	6.136%	$193.6345	$193.63	$193.65	$193.60
Purchase #7	$180.72	7.503%	$194.2794	$194.28	$194.30	$194.30
7 purchase totals =	$999.08		$1,061.6851	$1,061.68	$1,061.75	$1,061.70