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	$59.85	13.374%	$67.8543	$67.85	$67.85	$67.90
Purchase #2	$31.77	7.525%	$34.1607	$34.16	$34.15	$34.20
Purchase #3	$174.84	10.289%	$192.8293	$192.83	$192.85	$192.80
Purchase #4	$146.66	4.793%	$153.6894	$153.69	$153.70	$153.70
Purchase #5	$57.74	3.765%	$59.9139	$59.91	$59.90	$59.90
Purchase #6	$165.63	5.447%	$174.6519	$174.65	$174.65	$174.70
Purchase #7	$104.35	3.827%	$108.3435	$108.34	$108.35	$108.30
7 purchase totals =	$740.84		$791.4430	$791.43	$791.45	$791.50