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	$133.36	3.116%	$137.5155	$137.52	$137.50	$137.50
Purchase #2	$126.36	9.580%	$138.4653	$138.47	$138.45	$138.50
Purchase #3	$207.89	7.138%	$222.7292	$222.73	$222.75	$222.70
Purchase #4	$54.58	12.735%	$61.5308	$61.53	$61.55	$61.50
Purchase #5	$247.65	7.337%	$265.8201	$265.82	$265.80	$265.80
Purchase #6	$31.82	10.573%	$35.1843	$35.18	$35.20	$35.20
Purchase #7	$155.87	12.262%	$174.9828	$174.98	$175.00	$175.00
7 purchase totals =	$957.53		$1,036.2280	$1,036.23	$1,036.25	$1,036.20