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	$24.82	10.256%	$27.3655	$27.37	$27.35	$27.40
Purchase #2	$80.59	10.714%	$89.2244	$89.22	$89.20	$89.20
Purchase #3	$247.41	6.824%	$264.2933	$264.29	$264.30	$264.30
Purchase #4	$124.93	7.537%	$134.346	$134.35	$134.35	$134.30
Purchase #5	$57.29	7.195%	$61.412	$61.41	$61.40	$61.40
Purchase #6	$83.51	8.108%	$90.281	$90.28	$90.30	$90.30
Purchase #7	$210.66	10.338%	$232.438	$232.44	$232.45	$232.40
7 purchase totals =	$829.21		$899.3602	$899.36	$899.35	$899.30