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	$249.86	11.793%	$279.326	$279.33	$279.35	$279.30
Purchase #2	$97.25	10.358%	$107.3232	$107.32	$107.30	$107.30
Purchase #3	$197.67	7.767%	$213.023	$213.02	$213.00	$213.00
Purchase #4	$223.66	4.332%	$233.349	$233.35	$233.35	$233.30
Purchase #5	$104.33	7.486%	$112.1401	$112.14	$112.15	$112.10
Purchase #6	$39.89	13.472%	$45.264	$45.26	$45.25	$45.30
Purchase #7	$82.29	5.251%	$86.611	$86.61	$86.60	$86.60
7 purchase totals =	$994.95		$1,077.0363	$1,077.03	$1,077.00	$1,076.90