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	$120.96	6.542%	$128.8732	$128.87	$128.85	$128.90
Purchase #2	$153.67	11.619%	$171.5249	$171.52	$171.50	$171.50
Purchase #3	$138.86	6.189%	$147.454	$147.45	$147.45	$147.50
Purchase #4	$91.87	7.443%	$98.7079	$98.71	$98.70	$98.70
Purchase #5	$87.35	3.190%	$90.1365	$90.14	$90.15	$90.10
Purchase #6	$244.43	3.574%	$253.1659	$253.17	$253.15	$253.20
Purchase #7	$226.90	12.436%	$255.1173	$255.12	$255.10	$255.10
7 purchase totals =	$1,064.04		$1,144.9797	$1,144.98	$1,144.90	$1,145.00