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	$148.81	13.774%	$169.3071	$169.31	$169.30	$169.30
Purchase #2	$219.60	4.310%	$229.0648	$229.06	$229.05	$229.10
Purchase #3	$74.51	3.766%	$77.316	$77.32	$77.30	$77.30
Purchase #4	$144.71	13.527%	$164.2849	$164.28	$164.30	$164.30
Purchase #5	$171.27	4.178%	$178.4257	$178.43	$178.45	$178.40
Purchase #6	$6.75	11.710%	$7.5404	$7.54	$7.55	$7.50
Purchase #7	$28.58	8.559%	$31.0262	$31.03	$31.05	$31.00
7 purchase totals =	$794.23		$856.9651	$856.97	$857.00	$856.90