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	$137.50	12.752%	$155.034	$155.03	$155.05	$155.00
Purchase #2	$99.97	6.652%	$106.62	$106.62	$106.60	$106.60
Purchase #3	$196.98	3.215%	$203.3129	$203.31	$203.30	$203.30
Purchase #4	$92.32	8.147%	$99.8413	$99.84	$99.85	$99.80
Purchase #5	$234.27	3.182%	$241.7245	$241.72	$241.70	$241.70
Purchase #6	$29.25	13.755%	$33.2733	$33.27	$33.25	$33.30
Purchase #7	$156.40	7.649%	$168.363	$168.36	$168.35	$168.40
7 purchase totals =	$946.69		$1,008.1690	$1,008.15	$1,008.10	$1,008.10