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	$89.44	4.561%	$93.5194	$93.52	$93.50	$93.50
Purchase #2	$123.41	13.428%	$139.9815	$139.98	$140.00	$140.00
Purchase #3	$191.50	10.647%	$211.889	$211.89	$211.90	$211.90
Purchase #4	$60.52	10.341%	$66.7784	$66.78	$66.80	$66.80
Purchase #5	$18.72	9.782%	$20.5512	$20.55	$20.55	$20.60
Purchase #6	$188.76	3.346%	$195.0759	$195.08	$195.10	$195.10
Purchase #7	$48.46	4.472%	$50.6271	$50.63	$50.65	$50.60
7 purchase totals =	$720.81		$778.4225	$778.43	$778.50	$778.50