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	$135.43	4.263%	$141.2034	$141.20	$141.20	$141.20
Purchase #2	$51.70	10.835%	$57.3017	$57.30	$57.30	$57.30
Purchase #3	$173.30	8.592%	$188.1899	$188.19	$188.20	$188.20
Purchase #4	$55.66	12.635%	$62.6926	$62.69	$62.70	$62.70
Purchase #5	$124.76	9.695%	$136.8555	$136.86	$136.85	$136.90
Purchase #6	$95.51	4.221%	$99.5415	$99.54	$99.55	$99.50
Purchase #7	$61.76	6.579%	$65.8232	$65.82	$65.80	$65.80
7 purchase totals =	$698.12		$751.6078	$751.60	$751.60	$751.60