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	$18.78	13.490%	$21.3134	$21.31	$21.30	$21.30
Purchase #2	$135.30	13.751%	$153.9051	$153.91	$153.90	$153.90
Purchase #3	$58.62	12.334%	$65.8502	$65.85	$65.85	$65.90
Purchase #4	$68.72	11.824%	$76.8455	$76.85	$76.85	$76.80
Purchase #5	$169.79	9.456%	$185.8453	$185.85	$185.85	$185.80
Purchase #6	$98.79	13.656%	$112.2808	$112.28	$112.30	$112.30
Purchase #7	$169.25	9.138%	$184.7161	$184.72	$184.70	$184.70
7 purchase totals =	$719.25		$800.7564	$800.77	$800.75	$800.70