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	$94.33	8.371%	$102.2264	$102.23	$102.25	$102.20
Purchase #2	$211.86	3.433%	$219.1332	$219.13	$219.15	$219.10
Purchase #3	$96.94	4.588%	$101.3876	$101.39	$101.40	$101.40
Purchase #4	$38.48	5.457%	$40.5799	$40.58	$40.60	$40.60
Purchase #5	$127.44	7.784%	$137.3599	$137.36	$137.35	$137.40
Purchase #6	$135.91	3.798%	$141.0719	$141.07	$141.05	$141.10
Purchase #7	$182.31	7.815%	$196.5575	$196.56	$196.55	$196.60
7 purchase totals =	$887.27		$938.3164	$938.32	$938.35	$938.40