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	$45.74	12.321%	$51.3756	$51.38	$51.40	$51.40
Purchase #2	$60.31	8.812%	$65.6245	$65.62	$65.60	$65.60
Purchase #3	$79.53	4.457%	$83.0747	$83.07	$83.05	$83.10
Purchase #4	$89.50	12.509%	$100.6956	$100.70	$100.70	$100.70
Purchase #5	$231.36	7.603%	$248.9503	$248.95	$248.95	$249.00
Purchase #6	$232.37	11.851%	$259.9082	$259.91	$259.90	$259.90
Purchase #7	$198.52	11.702%	$221.7508	$221.75	$221.75	$221.80
7 purchase totals =	$937.33		$1,031.3797	$1,031.38	$1,031.35	$1,031.50