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	$46.40	8.471%	$50.3305	$50.33	$50.35	$50.30
Purchase #2	$56.43	3.793%	$58.5704	$58.57	$58.55	$58.60
Purchase #3	$131.81	9.663%	$144.5468	$144.55	$144.55	$144.50
Purchase #4	$10.33	6.695%	$11.0216	$11.02	$11.00	$11.00
Purchase #5	$148.49	11.668%	$165.8158	$165.82	$165.80	$165.80
Purchase #6	$156.63	6.866%	$167.3842	$167.38	$167.40	$167.40
Purchase #7	$55.65	12.552%	$62.6352	$62.64	$62.65	$62.60
7 purchase totals =	$605.74		$660.3045	$660.31	$660.30	$660.20