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	$126.29	10.770%	$139.8914	$139.89	$139.90	$139.90
Purchase #2	$83.81	8.737%	$91.1325	$91.13	$91.15	$91.10
Purchase #3	$140.73	13.782%	$160.1254	$160.13	$160.15	$160.10
Purchase #4	$250.25	9.565%	$274.1864	$274.19	$274.20	$274.20
Purchase #5	$181.31	8.321%	$196.3968	$196.40	$196.40	$196.40
Purchase #6	$150.55	9.767%	$165.2542	$165.25	$165.25	$165.30
Purchase #7	$102.92	7.485%	$110.6236	$110.62	$110.60	$110.60
7 purchase totals =	$1,035.86		$1,137.6103	$1,137.61	$1,137.65	$1,137.60