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	$243.80	12.184%	$273.5046	$273.50	$273.50	$273.50
Purchase #2	$187.31	13.501%	$212.5987	$212.60	$212.60	$212.60
Purchase #3	$197.40	4.711%	$206.6995	$206.70	$206.70	$206.70
Purchase #4	$56.46	5.498%	$59.5642	$59.56	$59.55	$59.60
Purchase #5	$200.82	7.277%	$215.4337	$215.43	$215.45	$215.40
Purchase #6	$15.89	10.127%	$17.4992	$17.50	$17.50	$17.50
Purchase #7	$151.50	13.356%	$171.7343	$171.73	$171.75	$171.70
7 purchase totals =	$1,053.18		$1,157.0342	$1,157.02	$1,157.05	$1,157.00