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	$89.74	10.382%	$99.0568	$99.06	$99.05	$99.10
Purchase #2	$226.98	13.339%	$257.2569	$257.26	$257.25	$257.30
Purchase #3	$185.58	10.766%	$205.5595	$205.56	$205.55	$205.60
Purchase #4	$6.72	7.650%	$7.2341	$7.23	$7.25	$7.20
Purchase #5	$78.32	9.398%	$85.6805	$85.68	$85.70	$85.70
Purchase #6	$166.75	12.684%	$187.9006	$187.90	$187.90	$187.90
Purchase #7	$125.54	4.451%	$131.1278	$131.13	$131.15	$131.10
7 purchase totals =	$879.63		$973.8162	$973.82	$973.85	$973.90