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	$5.60	9.594%	$6.1373	$6.14	$6.15	$6.10
Purchase #2	$225.30	6.605%	$240.1811	$240.18	$240.20	$240.20
Purchase #3	$233.88	9.155%	$255.2917	$255.29	$255.30	$255.30
Purchase #4	$131.86	5.606%	$139.2521	$139.25	$139.25	$139.30
Purchase #5	$85.45	4.611%	$89.3901	$89.39	$89.40	$89.40
Purchase #6	$100.99	9.134%	$110.2144	$110.21	$110.20	$110.20
Purchase #7	$110.72	4.246%	$115.4212	$115.42	$115.40	$115.40
7 purchase totals =	$893.80		$955.8879	$955.88	$955.90	$955.90