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	$233.82	10.867%	$259.2292	$259.23	$259.25	$259.20
Purchase #2	$109.56	10.185%	$120.7187	$120.72	$120.70	$120.70
Purchase #3	$72.90	10.622%	$80.6434	$80.64	$80.65	$80.60
Purchase #4	$130.39	9.265%	$142.4706	$142.47	$142.45	$142.50
Purchase #5	$17.77	6.575%	$18.9384	$18.94	$18.95	$18.90
Purchase #6	$184.43	3.148%	$190.2359	$190.24	$190.25	$190.20
Purchase #7	$113.29	10.871%	$125.6058	$125.61	$125.60	$125.60
7 purchase totals =	$862.16		$937.8420	$937.85	$937.85	$937.70