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	$181.59	3.857%	$188.5939	$188.59	$188.60	$188.60
Purchase #2	$205.78	13.346%	$233.2434	$233.24	$233.25	$233.20
Purchase #3	$76.49	12.729%	$86.2264	$86.23	$86.25	$86.20
Purchase #4	$84.85	5.560%	$89.5677	$89.57	$89.55	$89.60
Purchase #5	$211.81	12.519%	$238.3265	$238.33	$238.35	$238.30
Purchase #6	$171.30	6.828%	$182.9964	$183.00	$183.00	$183.00
Purchase #7	$47.82	10.580%	$52.8794	$52.88	$52.90	$52.90
7 purchase totals =	$979.64		$1,071.8337	$1,071.84	$1,071.90	$1,071.80