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	$76.28	6.240%	$81.0399	$81.04	$81.05	$81.00
Purchase #2	$143.39	13.368%	$162.5584	$162.56	$162.55	$162.60
Purchase #3	$161.84	13.557%	$183.7806	$183.78	$183.80	$183.80
Purchase #4	$137.25	9.504%	$150.2942	$150.29	$150.30	$150.30
Purchase #5	$61.39	4.767%	$64.3165	$64.32	$64.30	$64.30
Purchase #6	$176.47	7.846%	$190.3158	$190.32	$190.30	$190.30
Purchase #7	$133.37	13.236%	$151.0229	$151.02	$151.00	$151.00
7 purchase totals =	$889.99		$983.3283	$983.33	$983.30	$983.30