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	$128.82	13.648%	$146.4014	$146.40	$146.40	$146.40
Purchase #2	$56.70	9.467%	$62.0678	$62.07	$62.05	$62.10
Purchase #3	$36.39	9.363%	$39.7972	$39.80	$39.80	$39.80
Purchase #4	$100.25	7.279%	$107.5472	$107.55	$107.55	$107.50
Purchase #5	$61.36	4.309%	$64.004	$64.00	$64.00	$64.00
Purchase #6	$160.89	4.870%	$168.7253	$168.73	$168.75	$168.70
Purchase #7	$36.82	9.507%	$40.3205	$40.32	$40.30	$40.30
7 purchase totals =	$581.23		$628.8634	$628.87	$628.85	$628.80