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	$185.49	9.583%	$203.2655	$203.27	$203.25	$203.30
Purchase #2	$83.37	13.423%	$94.5608	$94.56	$94.55	$94.60
Purchase #3	$91.89	9.295%	$100.4312	$100.43	$100.45	$100.40
Purchase #4	$36.53	6.307%	$38.8339	$38.83	$38.85	$38.80
Purchase #5	$85.30	10.655%	$94.3887	$94.39	$94.40	$94.40
Purchase #6	$27.55	13.617%	$31.3015	$31.30	$31.30	$31.30
Purchase #7	$77.56	9.541%	$84.96	$84.96	$84.95	$85.00
7 purchase totals =	$587.69		$647.7416	$647.74	$647.75	$647.80