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	$123.73	13.666%	$140.6389	$140.64	$140.65	$140.60
Purchase #2	$220.32	8.146%	$238.2673	$238.27	$238.25	$238.30
Purchase #3	$99.84	11.201%	$111.0231	$111.02	$111.00	$111.00
Purchase #4	$129.83	11.709%	$145.0318	$145.03	$145.05	$145.00
Purchase #5	$55.98	11.116%	$62.2027	$62.20	$62.20	$62.20
Purchase #6	$102.43	11.331%	$114.0363	$114.04	$114.05	$114.00
Purchase #7	$170.32	8.193%	$184.2743	$184.27	$184.25	$184.30
7 purchase totals =	$902.45		$995.4744	$995.47	$995.45	$995.40