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	$137.37	3.166%	$141.7191	$141.72	$141.70	$141.70
Purchase #2	$115.45	10.799%	$127.9174	$127.92	$127.90	$127.90
Purchase #3	$81.40	10.269%	$89.759	$89.76	$89.75	$89.80
Purchase #4	$167.78	3.228%	$173.1959	$173.20	$173.20	$173.20
Purchase #5	$191.66	9.243%	$209.3751	$209.38	$209.40	$209.40
Purchase #6	$220.92	7.795%	$238.1407	$238.14	$238.15	$238.10
Purchase #7	$114.71	3.243%	$118.43	$118.43	$118.45	$118.40
7 purchase totals =	$1,029.29		$1,098.5372	$1,098.55	$1,098.55	$1,098.50