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	$128.37	8.553%	$139.3495	$139.35	$139.35	$139.30
Purchase #2	$124.76	5.604%	$131.7516	$131.75	$131.75	$131.80
Purchase #3	$188.60	11.182%	$209.6893	$209.69	$209.70	$209.70
Purchase #4	$206.48	8.202%	$223.4155	$223.42	$223.40	$223.40
Purchase #5	$166.44	3.630%	$172.4818	$172.48	$172.50	$172.50
Purchase #6	$154.68	7.368%	$166.0768	$166.08	$166.10	$166.10
Purchase #7	$122.68	13.371%	$139.0835	$139.08	$139.10	$139.10
7 purchase totals =	$1,092.01		$1,181.8480	$1,181.85	$1,181.90	$1,181.90