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	$166.92	13.225%	$188.9952	$189.00	$189.00	$189.00
Purchase #2	$223.91	11.202%	$248.9924	$248.99	$249.00	$249.00
Purchase #3	$119.46	10.853%	$132.425	$132.43	$132.45	$132.40
Purchase #4	$81.32	10.540%	$89.8911	$89.89	$89.90	$89.90
Purchase #5	$19.67	10.723%	$21.7792	$21.78	$21.80	$21.80
Purchase #6	$78.88	10.162%	$86.8958	$86.90	$86.90	$86.90
Purchase #7	$110.72	13.830%	$126.0326	$126.03	$126.05	$126.00
7 purchase totals =	$800.88		$895.0113	$895.02	$895.10	$895.00