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	$131.84	5.476%	$139.0596	$139.06	$139.05	$139.10
Purchase #2	$105.87	4.116%	$110.2276	$110.23	$110.25	$110.20
Purchase #3	$25.32	12.474%	$28.4784	$28.48	$28.50	$28.50
Purchase #4	$130.39	8.543%	$141.5292	$141.53	$141.55	$141.50
Purchase #5	$94.90	9.245%	$103.6735	$103.67	$103.65	$103.70
Purchase #6	$119.41	3.418%	$123.4914	$123.49	$123.50	$123.50
Purchase #7	$188.53	13.575%	$214.1229	$214.12	$214.10	$214.10
7 purchase totals =	$796.26		$860.5826	$860.58	$860.60	$860.60