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	$40.44	6.627%	$43.12	$43.12	$43.10	$43.10
Purchase #2	$120.64	4.741%	$126.3595	$126.36	$126.35	$126.40
Purchase #3	$65.76	10.759%	$72.8351	$72.84	$72.85	$72.80
Purchase #4	$132.28	11.800%	$147.889	$147.89	$147.90	$147.90
Purchase #5	$202.85	10.383%	$223.9119	$223.91	$223.90	$223.90
Purchase #6	$85.72	5.269%	$90.2366	$90.24	$90.25	$90.20
Purchase #7	$176.70	9.256%	$193.0554	$193.06	$193.05	$193.10
7 purchase totals =	$824.39		$897.4075	$897.42	$897.40	$897.40