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	$175.78	8.370%	$190.4928	$190.49	$190.50	$190.50
Purchase #2	$51.75	8.231%	$56.0095	$56.01	$56.00	$56.00
Purchase #3	$141.67	12.502%	$159.3816	$159.38	$159.40	$159.40
Purchase #4	$91.38	13.281%	$103.5162	$103.52	$103.50	$103.50
Purchase #5	$138.41	9.492%	$151.5479	$151.55	$151.55	$151.50
Purchase #6	$91.27	6.438%	$97.146	$97.15	$97.15	$97.10
Purchase #7	$80.27	12.538%	$90.3343	$90.33	$90.35	$90.30
7 purchase totals =	$770.53		$848.4283	$848.43	$848.45	$848.30