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	$138.25	3.372%	$142.9118	$142.91	$142.90	$142.90
Purchase #2	$99.75	11.426%	$111.1474	$111.15	$111.15	$111.10
Purchase #3	$92.90	13.796%	$105.7165	$105.72	$105.70	$105.70
Purchase #4	$100.52	5.790%	$106.3401	$106.34	$106.35	$106.30
Purchase #5	$22.90	3.682%	$23.7432	$23.74	$23.75	$23.70
Purchase #6	$181.60	8.369%	$196.7981	$196.80	$196.80	$196.80
Purchase #7	$175.48	11.732%	$196.0673	$196.07	$196.05	$196.10
7 purchase totals =	$811.40		$882.7244	$882.73	$882.70	$882.60