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	$37.28	6.585%	$39.7349	$39.73	$39.75	$39.70
Purchase #2	$38.26	13.746%	$43.5192	$43.52	$43.50	$43.50
Purchase #3	$61.63	4.736%	$64.5488	$64.55	$64.55	$64.50
Purchase #4	$118.39	4.107%	$123.2523	$123.25	$123.25	$123.30
Purchase #5	$155.92	8.278%	$168.8271	$168.83	$168.85	$168.80
Purchase #6	$165.43	7.712%	$178.188	$178.19	$178.20	$178.20
Purchase #7	$156.99	7.837%	$169.2933	$169.29	$169.30	$169.30
7 purchase totals =	$733.90		$787.3636	$787.36	$787.40	$787.30