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	$54.59	6.103%	$57.9216	$57.92	$57.90	$57.90
Purchase #2	$105.30	7.321%	$113.009	$113.01	$113.00	$113.00
Purchase #3	$117.39	12.260%	$131.782	$131.78	$131.80	$131.80
Purchase #4	$153.83	9.782%	$168.8777	$168.88	$168.90	$168.90
Purchase #5	$156.61	3.823%	$162.5972	$162.60	$162.60	$162.60
Purchase #6	$219.28	6.737%	$234.0529	$234.05	$234.05	$234.10
Purchase #7	$6.42	8.771%	$6.9831	$6.98	$7.00	$7.00
7 purchase totals =	$813.42		$875.2235	$875.22	$875.25	$875.30