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	$245.71	4.698%	$257.2535	$257.25	$257.25	$257.30
Purchase #2	$181.96	3.138%	$187.6699	$187.67	$187.65	$187.70
Purchase #3	$208.67	11.736%	$233.1595	$233.16	$233.15	$233.20
Purchase #4	$169.76	3.434%	$175.5896	$175.59	$175.60	$175.60
Purchase #5	$89.35	10.240%	$98.4994	$98.50	$98.50	$98.50
Purchase #6	$28.86	9.809%	$31.6909	$31.69	$31.70	$31.70
Purchase #7	$89.67	8.619%	$97.3987	$97.40	$97.40	$97.40
7 purchase totals =	$1,013.98		$1,081.2615	$1,081.26	$1,081.25	$1,081.40