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	$55.36	12.760%	$62.4239	$62.42	$62.40	$62.40
Purchase #2	$22.34	9.510%	$24.4645	$24.46	$24.45	$24.50
Purchase #3	$117.32	11.705%	$131.0523	$131.05	$131.05	$131.10
Purchase #4	$144.58	6.851%	$154.4852	$154.49	$154.50	$154.50
Purchase #5	$88.99	5.546%	$93.9254	$93.93	$93.95	$93.90
Purchase #6	$90.70	8.699%	$98.59	$98.59	$98.60	$98.60
Purchase #7	$26.47	7.240%	$28.3864	$28.39	$28.40	$28.40
7 purchase totals =	$545.76		$593.3277	$593.33	$593.35	$593.40