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	$138.81	10.285%	$153.0866	$153.09	$153.10	$153.10
Purchase #2	$45.37	11.269%	$50.4827	$50.48	$50.50	$50.50
Purchase #3	$169.88	12.744%	$191.5295	$191.53	$191.55	$191.50
Purchase #4	$57.77	10.241%	$63.6862	$63.69	$63.70	$63.70
Purchase #5	$240.63	8.205%	$260.3737	$260.37	$260.35	$260.40
Purchase #6	$149.54	4.421%	$156.1512	$156.15	$156.15	$156.20
Purchase #7	$129.90	9.368%	$142.069	$142.07	$142.05	$142.10
7 purchase totals =	$931.90		$1,017.3789	$1,017.38	$1,017.40	$1,017.50