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	$51.42	7.109%	$55.0754	$55.08	$55.10	$55.10
Purchase #2	$104.98	8.161%	$113.5474	$113.55	$113.55	$113.50
Purchase #3	$21.79	12.841%	$24.5881	$24.59	$24.60	$24.60
Purchase #4	$233.71	11.109%	$259.6728	$259.67	$259.65	$259.70
Purchase #5	$193.70	13.312%	$219.4853	$219.49	$219.50	$219.50
Purchase #6	$82.27	8.356%	$89.1445	$89.14	$89.15	$89.10
Purchase #7	$165.41	13.871%	$188.354	$188.35	$188.35	$188.40
7 purchase totals =	$853.28		$949.8675	$949.87	$949.90	$949.90