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	$229.64	3.163%	$236.9035	$236.90	$236.90	$236.90
Purchase #2	$83.27	8.468%	$90.3213	$90.32	$90.30	$90.30
Purchase #3	$103.61	8.317%	$112.2272	$112.23	$112.25	$112.20
Purchase #4	$155.85	8.347%	$168.8588	$168.86	$168.85	$168.90
Purchase #5	$135.39	4.273%	$141.1752	$141.18	$141.20	$141.20
Purchase #6	$103.41	10.414%	$114.1791	$114.18	$114.20	$114.20
Purchase #7	$118.74	10.557%	$131.2754	$131.28	$131.30	$131.30
7 purchase totals =	$929.91		$994.9405	$994.95	$995.00	$995.00