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	$238.57	3.473%	$246.8555	$246.86	$246.85	$246.90
Purchase #2	$178.45	10.542%	$197.2622	$197.26	$197.25	$197.30
Purchase #3	$156.25	7.597%	$168.1203	$168.12	$168.10	$168.10
Purchase #4	$122.50	6.603%	$130.5887	$130.59	$130.60	$130.60
Purchase #5	$78.80	13.102%	$89.1244	$89.12	$89.10	$89.10
Purchase #6	$9.32	10.853%	$10.3315	$10.33	$10.35	$10.30
Purchase #7	$65.44	3.180%	$67.521	$67.52	$67.50	$67.50
7 purchase totals =	$849.33		$909.8036	$909.80	$909.75	$909.80