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	$142.39	5.564%	$150.3126	$150.31	$150.30	$150.30
Purchase #2	$29.66	6.845%	$31.6902	$31.69	$31.70	$31.70
Purchase #3	$149.57	4.800%	$156.7494	$156.75	$156.75	$156.70
Purchase #4	$119.77	6.134%	$127.1167	$127.12	$127.10	$127.10
Purchase #5	$81.73	9.690%	$89.6496	$89.65	$89.65	$89.60
Purchase #6	$211.39	13.603%	$240.1454	$240.15	$240.15	$240.10
Purchase #7	$118.61	12.296%	$133.1943	$133.19	$133.20	$133.20
7 purchase totals =	$853.12		$928.8582	$928.86	$928.85	$928.70