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	$111.96	10.610%	$123.839	$123.84	$123.85	$123.80
Purchase #2	$240.40	13.448%	$272.729	$272.73	$272.75	$272.70
Purchase #3	$182.55	9.171%	$199.2917	$199.29	$199.30	$199.30
Purchase #4	$213.25	11.662%	$238.1192	$238.12	$238.10	$238.10
Purchase #5	$170.28	5.225%	$179.1771	$179.18	$179.20	$179.20
Purchase #6	$179.33	9.674%	$196.6784	$196.68	$196.70	$196.70
Purchase #7	$92.39	3.150%	$95.3003	$95.30	$95.30	$95.30
7 purchase totals =	$1,190.16		$1,305.1347	$1,305.14	$1,305.20	$1,305.10