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	$85.91	5.377%	$90.5294	$90.53	$90.55	$90.50
Purchase #2	$134.79	3.215%	$139.1235	$139.12	$139.10	$139.10
Purchase #3	$89.68	9.848%	$98.5117	$98.51	$98.50	$98.50
Purchase #4	$167.96	6.857%	$179.477	$179.48	$179.50	$179.50
Purchase #5	$138.76	6.569%	$147.8751	$147.88	$147.90	$147.90
Purchase #6	$235.94	8.683%	$256.4267	$256.43	$256.45	$256.40
Purchase #7	$38.60	10.813%	$42.7738	$42.77	$42.75	$42.80
7 purchase totals =	$891.64		$954.7172	$954.72	$954.75	$954.70