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	$126.44	8.860%	$137.6426	$137.64	$137.65	$137.60
Purchase #2	$83.60	10.223%	$92.1464	$92.15	$92.15	$92.10
Purchase #3	$89.31	7.159%	$95.7037	$95.70	$95.70	$95.70
Purchase #4	$239.25	13.284%	$271.032	$271.03	$271.05	$271.00
Purchase #5	$45.38	4.535%	$47.438	$47.44	$47.45	$47.40
Purchase #6	$136.72	3.243%	$141.1538	$141.15	$141.15	$141.20
Purchase #7	$130.32	6.836%	$139.2287	$139.23	$139.25	$139.20
7 purchase totals =	$851.02		$924.3452	$924.34	$924.40	$924.20