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	$248.39	6.803%	$265.288	$265.29	$265.30	$265.30
Purchase #2	$122.86	12.531%	$138.2556	$138.26	$138.25	$138.30
Purchase #3	$124.59	12.818%	$140.5599	$140.56	$140.55	$140.60
Purchase #4	$116.51	13.144%	$131.8241	$131.82	$131.80	$131.80
Purchase #5	$245.65	3.538%	$254.3411	$254.34	$254.35	$254.30
Purchase #6	$29.81	4.334%	$31.102	$31.10	$31.10	$31.10
Purchase #7	$142.74	10.788%	$158.1388	$158.14	$158.15	$158.10
7 purchase totals =	$1,030.55		$1,119.5095	$1,119.51	$1,119.50	$1,119.50