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	$79.35	6.149%	$84.2292	$84.23	$84.25	$84.20
Purchase #2	$201.58	4.750%	$211.1551	$211.16	$211.15	$211.20
Purchase #3	$28.32	10.241%	$31.2203	$31.22	$31.20	$31.20
Purchase #4	$55.69	6.439%	$59.2759	$59.28	$59.30	$59.30
Purchase #5	$137.56	3.643%	$142.5713	$142.57	$142.55	$142.60
Purchase #6	$129.90	10.136%	$143.0667	$143.07	$143.05	$143.10
Purchase #7	$104.82	9.390%	$114.6626	$114.66	$114.65	$114.70
7 purchase totals =	$737.22		$786.1811	$786.19	$786.15	$786.30