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	$222.37	9.366%	$243.1972	$243.20	$243.20	$243.20
Purchase #2	$15.82	4.152%	$16.4768	$16.48	$16.50	$16.50
Purchase #3	$215.84	4.582%	$225.7298	$225.73	$225.75	$225.70
Purchase #4	$90.27	4.539%	$94.3674	$94.37	$94.35	$94.40
Purchase #5	$70.31	12.132%	$78.84	$78.84	$78.85	$78.80
Purchase #6	$242.34	12.823%	$273.4153	$273.42	$273.40	$273.40
Purchase #7	$131.94	12.596%	$148.5592	$148.56	$148.55	$148.60
7 purchase totals =	$988.89		$1,080.5857	$1,080.60	$1,080.60	$1,080.60