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	$207.84	9.302%	$227.1733	$227.17	$227.15	$227.20
Purchase #2	$130.58	8.818%	$142.0945	$142.09	$142.10	$142.10
Purchase #3	$74.96	10.152%	$82.5699	$82.57	$82.55	$82.60
Purchase #4	$137.59	9.840%	$151.1289	$151.13	$151.15	$151.10
Purchase #5	$81.76	10.779%	$90.5729	$90.57	$90.55	$90.60
Purchase #6	$54.87	8.119%	$59.3249	$59.32	$59.30	$59.30
Purchase #7	$212.41	7.768%	$228.91	$228.91	$228.90	$228.90
7 purchase totals =	$900.01		$981.7744	$981.76	$981.70	$981.80