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	$12.49	5.530%	$13.1807	$13.18	$13.20	$13.20
Purchase #2	$238.44	3.320%	$246.3562	$246.36	$246.35	$246.40
Purchase #3	$195.59	11.623%	$218.3234	$218.32	$218.30	$218.30
Purchase #4	$95.90	3.813%	$99.5567	$99.56	$99.55	$99.60
Purchase #5	$69.93	12.362%	$78.5747	$78.57	$78.55	$78.60
Purchase #6	$230.78	11.121%	$256.445	$256.45	$256.45	$256.40
Purchase #7	$165.28	5.140%	$173.7754	$173.78	$173.80	$173.80
7 purchase totals =	$1,008.41		$1,086.2121	$1,086.22	$1,086.20	$1,086.30