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	$219.52	8.579%	$238.3526	$238.35	$238.35	$238.40
Purchase #2	$123.48	13.711%	$140.4103	$140.41	$140.40	$140.40
Purchase #3	$45.50	9.499%	$49.822	$49.82	$49.80	$49.80
Purchase #4	$90.52	8.869%	$98.5482	$98.55	$98.55	$98.50
Purchase #5	$125.72	9.283%	$137.3906	$137.39	$137.40	$137.40
Purchase #6	$40.78	3.185%	$42.0788	$42.08	$42.10	$42.10
Purchase #7	$189.82	12.580%	$213.6994	$213.70	$213.70	$213.70
7 purchase totals =	$835.34		$920.3019	$920.30	$920.30	$920.30