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	$90.25	13.390%	$102.3345	$102.33	$102.35	$102.30
Purchase #2	$113.51	12.510%	$127.7101	$127.71	$127.70	$127.70
Purchase #3	$223.47	8.845%	$243.2359	$243.24	$243.25	$243.20
Purchase #4	$128.82	3.820%	$133.7409	$133.74	$133.75	$133.70
Purchase #5	$61.81	6.622%	$65.9031	$65.90	$65.90	$65.90
Purchase #6	$91.41	12.803%	$103.1132	$103.11	$103.10	$103.10
Purchase #7	$212.75	7.222%	$228.1148	$228.11	$228.10	$228.10
7 purchase totals =	$922.02		$1,004.1525	$1,004.14	$1,004.15	$1,004.00