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	$226.88	12.605%	$255.4782	$255.48	$255.50	$255.50
Purchase #2	$90.83	9.433%	$99.398	$99.40	$99.40	$99.40
Purchase #3	$190.69	9.773%	$209.3261	$209.33	$209.35	$209.30
Purchase #4	$83.48	3.444%	$86.3551	$86.36	$86.35	$86.40
Purchase #5	$54.91	10.275%	$60.552	$60.55	$60.55	$60.60
Purchase #6	$239.62	13.244%	$271.3553	$271.36	$271.35	$271.40
Purchase #7	$166.56	11.841%	$186.2824	$186.28	$186.30	$186.30
7 purchase totals =	$1,052.97		$1,168.7471	$1,168.76	$1,168.80	$1,168.90