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	$7.64	3.461%	$7.9044	$7.90	$7.90	$7.90
Purchase #2	$189.64	5.685%	$200.421	$200.42	$200.40	$200.40
Purchase #3	$85.98	4.137%	$89.537	$89.54	$89.55	$89.50
Purchase #4	$213.58	11.175%	$237.4476	$237.45	$237.45	$237.40
Purchase #5	$233.54	9.461%	$255.6352	$255.64	$255.65	$255.60
Purchase #6	$73.75	12.275%	$82.8028	$82.80	$82.80	$82.80
Purchase #7	$166.55	12.643%	$187.6069	$187.61	$187.60	$187.60
7 purchase totals =	$970.68		$1,061.3549	$1,061.36	$1,061.35	$1,061.20