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	$81.32	5.142%	$85.5015	$85.50	$85.50	$85.50
Purchase #2	$175.91	11.469%	$196.0851	$196.09	$196.10	$196.10
Purchase #3	$174.37	4.279%	$181.8313	$181.83	$181.85	$181.80
Purchase #4	$211.54	13.631%	$240.375	$240.38	$240.40	$240.40
Purchase #5	$18.28	10.576%	$20.2133	$20.21	$20.20	$20.20
Purchase #6	$169.58	10.474%	$187.3418	$187.34	$187.35	$187.30
Purchase #7	$151.30	9.851%	$166.2046	$166.20	$166.20	$166.20
7 purchase totals =	$982.30		$1,077.5526	$1,077.55	$1,077.60	$1,077.50