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	$207.54	8.662%	$225.5171	$225.52	$225.50	$225.50
Purchase #2	$31.71	9.446%	$34.7053	$34.71	$34.70	$34.70
Purchase #3	$139.44	10.454%	$154.0171	$154.02	$154.00	$154.00
Purchase #4	$209.52	12.553%	$235.821	$235.82	$235.80	$235.80
Purchase #5	$144.30	5.560%	$152.3231	$152.32	$152.30	$152.30
Purchase #6	$145.37	5.622%	$153.5427	$153.54	$153.55	$153.50
Purchase #7	$40.29	7.746%	$43.4109	$43.41	$43.40	$43.40
7 purchase totals =	$918.17		$999.3372	$999.34	$999.25	$999.20