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	$139.42	4.457%	$145.6339	$145.63	$145.65	$145.60
Purchase #2	$151.78	10.516%	$167.7412	$167.74	$167.75	$167.70
Purchase #3	$219.36	8.501%	$238.0078	$238.01	$238.00	$238.00
Purchase #4	$90.52	9.746%	$99.3421	$99.34	$99.35	$99.30
Purchase #5	$160.95	12.687%	$181.3697	$181.37	$181.35	$181.40
Purchase #6	$195.29	12.168%	$219.0529	$219.05	$219.05	$219.10
Purchase #7	$13.61	12.689%	$15.337	$15.34	$15.35	$15.30
7 purchase totals =	$970.93		$1,066.4846	$1,066.48	$1,066.50	$1,066.40