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	$79.84	13.224%	$90.398	$90.40	$90.40	$90.40
Purchase #2	$244.99	5.723%	$259.0108	$259.01	$259.00	$259.00
Purchase #3	$14.57	3.474%	$15.0762	$15.08	$15.10	$15.10
Purchase #4	$241.90	3.719%	$250.8963	$250.90	$250.90	$250.90
Purchase #5	$118.45	9.631%	$129.8579	$129.86	$129.85	$129.90
Purchase #6	$144.29	4.435%	$150.6893	$150.69	$150.70	$150.70
Purchase #7	$172.70	13.588%	$196.1665	$196.17	$196.15	$196.20
7 purchase totals =	$1,016.74		$1,092.0950	$1,092.11	$1,092.10	$1,092.20