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	$48.41	13.234%	$54.8166	$54.82	$54.80	$54.80
Purchase #2	$250.69	11.136%	$278.6068	$278.61	$278.60	$278.60
Purchase #3	$77.78	4.144%	$81.0032	$81.00	$81.00	$81.00
Purchase #4	$26.39	11.481%	$29.4198	$29.42	$29.40	$29.40
Purchase #5	$26.30	4.442%	$27.4682	$27.47	$27.45	$27.50
Purchase #6	$84.35	7.454%	$90.6374	$90.64	$90.65	$90.60
Purchase #7	$26.94	4.508%	$28.1545	$28.15	$28.15	$28.20
7 purchase totals =	$540.86		$590.1065	$590.11	$590.05	$590.10