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	$229.55	13.170%	$259.7817	$259.78	$259.80	$259.80
Purchase #2	$40.33	6.397%	$42.9099	$42.91	$42.90	$42.90
Purchase #3	$68.60	11.515%	$76.4993	$76.50	$76.50	$76.50
Purchase #4	$133.64	5.369%	$140.8151	$140.82	$140.80	$140.80
Purchase #5	$133.46	4.504%	$139.471	$139.47	$139.45	$139.50
Purchase #6	$25.71	10.335%	$28.3671	$28.37	$28.35	$28.40
Purchase #7	$200.47	5.420%	$211.3355	$211.34	$211.35	$211.30
7 purchase totals =	$831.76		$899.1796	$899.19	$899.15	$899.20