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	$35.99	5.786%	$38.0724	$38.07	$38.05	$38.10
Purchase #2	$163.56	11.532%	$182.4217	$182.42	$182.40	$182.40
Purchase #3	$183.66	4.284%	$191.528	$191.53	$191.55	$191.50
Purchase #4	$60.56	3.577%	$62.7262	$62.73	$62.75	$62.70
Purchase #5	$188.83	12.223%	$211.9107	$211.91	$211.90	$211.90
Purchase #6	$172.35	10.832%	$191.019	$191.02	$191.00	$191.00
Purchase #7	$56.47	9.816%	$62.0131	$62.01	$62.00	$62.00
7 purchase totals =	$861.42		$939.6911	$939.69	$939.65	$939.60