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	$249.48	3.708%	$258.7307	$258.73	$258.75	$258.70
Purchase #2	$105.28	4.121%	$109.6186	$109.62	$109.60	$109.60
Purchase #3	$83.43	7.422%	$89.6222	$89.62	$89.60	$89.60
Purchase #4	$27.43	3.113%	$28.2839	$28.28	$28.30	$28.30
Purchase #5	$67.60	9.291%	$73.8807	$73.88	$73.90	$73.90
Purchase #6	$223.90	10.870%	$248.2379	$248.24	$248.25	$248.20
Purchase #7	$163.68	4.244%	$170.6266	$170.63	$170.65	$170.60
7 purchase totals =	$920.80		$979.0006	$979.00	$979.05	$978.90