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	$173.87	6.695%	$185.5106	$185.51	$185.50	$185.50
Purchase #2	$93.51	5.678%	$98.8195	$98.82	$98.80	$98.80
Purchase #3	$69.61	13.544%	$79.038	$79.04	$79.05	$79.00
Purchase #4	$123.45	10.234%	$136.0839	$136.08	$136.10	$136.10
Purchase #5	$198.53	12.160%	$222.6712	$222.67	$222.65	$222.70
Purchase #6	$55.99	10.402%	$61.8141	$61.81	$61.80	$61.80
Purchase #7	$127.67	11.106%	$141.849	$141.85	$141.85	$141.80
7 purchase totals =	$842.63		$925.7863	$925.78	$925.75	$925.70