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	$36.52	11.524%	$40.7286	$40.73	$40.75	$40.70
Purchase #2	$94.88	10.300%	$104.6526	$104.65	$104.65	$104.70
Purchase #3	$174.28	9.866%	$191.4745	$191.47	$191.45	$191.50
Purchase #4	$61.49	4.656%	$64.353	$64.35	$64.35	$64.40
Purchase #5	$139.43	9.631%	$152.8585	$152.86	$152.85	$152.90
Purchase #6	$166.38	9.864%	$182.7917	$182.79	$182.80	$182.80
Purchase #7	$237.80	11.136%	$264.2814	$264.28	$264.30	$264.30
7 purchase totals =	$910.78		$1,001.1403	$1,001.13	$1,001.15	$1,001.30