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	$54.80	5.165%	$57.6304	$57.63	$57.65	$57.60
Purchase #2	$220.56	10.339%	$243.3637	$243.36	$243.35	$243.40
Purchase #3	$30.78	9.126%	$33.589	$33.59	$33.60	$33.60
Purchase #4	$235.89	12.766%	$266.0037	$266.00	$266.00	$266.00
Purchase #5	$98.89	6.512%	$105.3297	$105.33	$105.35	$105.30
Purchase #6	$47.54	8.394%	$51.5305	$51.53	$51.55	$51.50
Purchase #7	$136.93	6.536%	$145.8797	$145.88	$145.90	$145.90
7 purchase totals =	$825.39		$903.3267	$903.32	$903.40	$903.30