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	$27.31	5.840%	$28.9049	$28.90	$28.90	$28.90
Purchase #2	$122.73	5.504%	$129.4851	$129.49	$129.50	$129.50
Purchase #3	$142.26	3.558%	$147.3216	$147.32	$147.30	$147.30
Purchase #4	$103.73	4.624%	$108.5265	$108.53	$108.55	$108.50
Purchase #5	$128.96	8.446%	$139.852	$139.85	$139.85	$139.90
Purchase #6	$151.32	7.680%	$162.9414	$162.94	$162.95	$162.90
Purchase #7	$27.25	3.486%	$28.1999	$28.20	$28.20	$28.20
7 purchase totals =	$703.56		$745.2314	$745.23	$745.25	$745.20