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	$123.86	11.633%	$138.2686	$138.27	$138.25	$138.30
Purchase #2	$110.94	4.156%	$115.5507	$115.55	$115.55	$115.60
Purchase #3	$130.82	8.431%	$141.8494	$141.85	$141.85	$141.80
Purchase #4	$175.42	11.759%	$196.0476	$196.05	$196.05	$196.00
Purchase #5	$95.31	3.176%	$98.337	$98.34	$98.35	$98.30
Purchase #6	$200.86	12.169%	$225.3027	$225.30	$225.30	$225.30
Purchase #7	$177.33	4.439%	$185.2017	$185.20	$185.20	$185.20
7 purchase totals =	$1,014.54		$1,100.5577	$1,100.56	$1,100.55	$1,100.50