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	$55.52	11.372%	$61.8337	$61.83	$61.85	$61.80
Purchase #2	$22.32	11.809%	$24.9558	$24.96	$24.95	$25.00
Purchase #3	$150.86	11.786%	$168.6404	$168.64	$168.65	$168.60
Purchase #4	$185.46	6.130%	$196.8287	$196.83	$196.85	$196.80
Purchase #5	$12.26	9.491%	$13.4236	$13.42	$13.40	$13.40
Purchase #6	$71.86	10.165%	$79.1646	$79.16	$79.15	$79.20
Purchase #7	$88.92	6.146%	$94.385	$94.39	$94.40	$94.40
7 purchase totals =	$587.20		$639.2318	$639.23	$639.25	$639.20