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	$180.96	4.193%	$188.5477	$188.55	$188.55	$188.50
Purchase #2	$98.88	3.535%	$102.3754	$102.38	$102.40	$102.40
Purchase #3	$108.80	5.501%	$114.7851	$114.79	$114.80	$114.80
Purchase #4	$131.31	6.406%	$139.7217	$139.72	$139.70	$139.70
Purchase #5	$78.38	8.607%	$85.1262	$85.13	$85.15	$85.10
Purchase #6	$159.76	9.871%	$175.5299	$175.53	$175.55	$175.50
Purchase #7	$36.44	3.498%	$37.7147	$37.71	$37.70	$37.70
7 purchase totals =	$794.53		$843.8007	$843.81	$843.85	$843.70